The Juggernaut has been the victim of this since Chuck Austen got a hold of him. Despite being a mass-murderer, a terrorist (he did destroy one of the WTC towers) and a sociopath who cares nothing for all the death and destruction he has caused. Who mainly concerns himself with his own gratification. You get one writer who portrays him as not having killed anyone on purpose and is just a misunderstood bully. Then people come out of the wood work to explain his actions. Going so far as to say him not actively doing something evil is proof of his heroic qualities that were there the whole time.
Jason Todd, while not without reason, was the main antagonist in Battle for the Cowl. While some may disagree with writer Tony Daniel's reasoning behind it, some are going as far to say he should have been Batman while Dick Grayson shouldn't. This despite the fact he was a Gun Trotting Batman in the mini series and he willingly killed before that. The very thing the original would never have stood for. The fact that he was voiced by Jensen Ackles in the Under The Red Hood movie likely playing a part in it too. Many, many fangirls are completely willing to overlook or "justify" the fact that he has brutally murdered people by saying that his victims deserved it or that he just needs a hug because he's just so cute and troubled! Fans get outraged whenever it's suggested, in-universe or out, that he should maybe be punished for his crimes. Because it's totally not his fault he picked that gun up and put a bullet in that dude's skull.
Damian has undergone character development but some of the fanart draws too much attention to the fact that he is ten and not that he gotTraining from Hell. He has killed a man and even very nearly killed Tim Drake before becoming Robin.
Larfleeze the Orange Lantern is a murderer who makes slaves of those he kills - but to comics fans, he's also a misunderstood softie who would almost certainly give up his greedy ways and totally be your friend if given the chance! The comics' art slightly reflects this, with Larfleeze getting cuter and less monstrous as time goes by, and his own comic reveals that he's had a Hilariously Abusive Childhood.
Ironically, ever since Civil War and House of M, Tony Stark's popularity has exploded among the fangirls. Granted, this may have something to do with the release of The Movie, but the seemingly insane fannishness predates even that...but not by much, since while he was always popular before Civil War, he was a relatively obscure figure compared to the household names of the X-Men and Spider-Man. So yeah...
It can also be argued that the opposite happened to Maddie - she's a mostly blameless woman who had a moment of selfishness while she thought she was dreaming, and has been written off as evil in canon ever since. Probably half the X-Men have tried to do similar things while possessed.
Dark Reign gave Bullseye and Mac Gargan (Venom III) fangirls, thanks to the Ho Yay they had with Daken. For that matter, the Dark Avengers as a whole got this treatment from fans and Dark Avengers was a popular book. Hell, some fans say Norman Osborn did a better job as "top cop" than Iron Man.
Also, Moonstone. Even though she's a therapist who used to make her patients off themselves for fun and stole her superpowers from another patient, a lot of fans like her Magnificent Bastard nature, and because, well, they find herdamn sexy. Hell, the character has reached Memetic Sex Goddess status in some circles of fandom.
Doctor Doom has received treatment of this nature from the fans. He is a complex Evil Overlord with a strong (if warped) sense of nobility and a tendency towards frequent Bad AssAwesome Moments, but he is still a villain. For example; the image of 'Doom as benevolent dictator' partially stems from a one-off book, Emperor Doom, in which Doom manages to conquer the Earth and begins to make numerous improvements in how things are run; this book is often used to reinforce the impression that Doom would be a great and benevolent leader if he managed to take over. However, he manages this largely by brainwashing the entire planet into accepting his rule (goodbye, freedom of thought and dissent); and he ultimately gives it up and lets the heroes defeat him because he gets bored, suggesting that he's ultimately not as interested in 'making the world a better place for all' as many would like to think. And yet some create an exaggerated ideal of how noble and benevolent . His vanity, insecurity, egomania, and brutality tend to be underplayed or ignored and writers who attempt to stress Doom's less-attractive qualities can be rejected vitriolically. Doom so embodies this characteristic that people actually brush off his actions in Avengers: The Children's Crusade where he kills the teenage Cassie Lang and takes the credit for Avengers Disassembled and House of M or the story "Unthinkable" where he murders his ex-love for demonic power and again attacks the Richards family, including possessing Valeria - just to hurt the patriarch.
Willy Pete from Empowered becomes an in-universe example of this after a video of him massacring (and in some cases raping) nearly a dozen superheroes leaks to the internet. People begin drawing yaoi doujinshi of him and the heroes he either injured, raped, or killed. Even another female superhero speaks well of him and adoringly downloads the doujinshi, brushing off his atrocities by saying that she didn't like the personalities of those he raped and killed anyway.
In the DCnU reboot, The Joker becomes an in-universe example after he disappears leaving only his face behind while Batman suffers in-universe Ron the Death Eater treatment. Suddenly Gothamites think Joker is a sympathetic murder victim and Batman is a heartless murderer who needs to be brought to justice. Somewhat retconned, in that it's later revealed that a significant amount of the protest in question was made up of people who usually either form his henchmen, or use his sprees as an excuse to go Axe Crazy.
Jhonen Vasquez seems to have an accidental habit of making these. His first creation, Johnny C has an insane amount of fangirls who claim that he's just misunderstood and lonely. It's true: most of Nny's prominent victims are assholes, the world is decidedly Crapsack, and he does get a few Pet the Dog moments (notably with Squee). Yet this overlooks that Johnny is schizophrenic, psychotic, sociopathic, and Ax-Crazy; that he killed an entire restaurant full of people because someone said he "looked wacky"; he has entire torture chambers in his Torture Cellar that contain who-knows-how-many people; he tried to murder the one girl who really liked him and drove her to become a recluse and hide in her apartment almost 24/7 out of paranoia; and he has killed numerous people for various insane reasons.
To get into even weirder territory, one-shot character Jimmy has a surprising number of fans who adore him (and some pair him up with Nny). They ignore that Jimmy killed people to imitate Johnny's "murderous style" and to get his attention. Not only that, but he was the person who brutally raped and killed a cheerleader, which crime Johnny was accused of in an earlier issue. And there's also Johnny's distaste for Jimmy and what he's done:
"You fucking idiot!! Admire me?!! You shit!!! I'm the villain in this fucking story!"
Ragamuffin gets this treatment from fangirls who claim that he's so cute when he's a rag doll and that he is hot when he's in his human-vampire form. The first animated episode in which he appears features him eating a girl alive. Probably the Heel-Face Turn he does for Lenore convinced the fans to consider him one of the most likeable characters in the comics.
Imagine you have a teddy bear or a cute plushie that you carry around all day. Now, what if that plushie has a life on its own, and it's a mysterious young guy who protects you from bad things? What if that guy is a good-lookingVampire? For some, this may be terrifying; for others, this is pure Fetish Fuel.
Lex Luthor has gotten some love ever since Lex Luthor: Man of Steel (well, mostly since), which tells a Superman story from his point of view and sees him rationalise his actions as Beware the Superman, with Lex seeing himself as the Only Sane Man on Earth who sees that humanity is becoming dependant on an untrustworthy, godlike alien whose mere presence will ultimately result in a stagnating and static civilization as nothing innovators like him create would be worth a jot next to the hero. Adding to the contrast is Superman rescuing the Toyman from an angry mob after he blew up a daycare centre and doing other things that were making him a Hero with Bad Publicity. However, the fans who side with him on this for his apparant humanist sympathies tend to overlook the fact that everything that happened in the story- including the daycare centre bombing- was secretly his doing and part of a grander plan to discredit and humiliate Superman- that he really does believe himself to be the hero doesn't make him good, it just makes him batshit insane. Not to mention that, for all his supposed humanism, he is ultimately a bigger threat to humanity than Superman ever would be — he certainly has a lot more of them killed throughout the story.
In the story "Mad Love," Harley Quinn was obviously believing this in-story about The Joker before her own descent into madness.
Lampshaded in Miracleman with the "Bateses", a subculture that identifies itself with the supervillain Kid Miracleman/Johnny Bates. This idolization occurs after Bates personally murders most of London and the surrounding countryside in grotesque and grisly fashion. We're talking grade-A horrific here, easily. This is likely a parody of real-life skinheads and Neo-Nazis, who became popular in Britain and greater Europe a generation or so after WWII.
Brian Azzarello was surprised and disturbed to find that the violent, amoral homicidal rapist and torturer Lono had a devoted fan following. There are Lono fangirls. That's right: Lono. Fangirls.
Venom. The alien symbiotes' "costumes" are emotionally striking in very different ways to different people and it's not fully certain whether they are Draco in Leather Pants, in which the characters' brutal acts are handwaved or rationalized, or Evil Is Sexy. Venom's (Eddie Brock's) Never Hurt an Innocentvow helps with the leather pants-ing. Though that still ignores that Brock HAS killed innocent people if they were in his way.
Carnage, however, there is no excuse for. He was even a serial killer before getting the symbiote.
Peter's Mean Boss at The Daily Bugle J. Jonah Jameson is an odd case. Fans usually side with Spidey whenever he acts like an Ungrateful Bastard and unfairly makes accusations against the hero. (Usually.) However, if there is even a hint that Jonah has been kidnapped, hurt, conned, or - God forbid - killed, fans never fail to send in mail showing support, concern, or outrage, whichever is appropriate. (It seems that, Jonah is thorn in the hero's side that fans just don't want to see go away.)
Teen Titans has Eric Forrester, an "emotional vampire" type of villain in a late '80s arc who preyed on women and would drain them of their souls for power, after making them sleep with him. While even the story states that he didn't really love Raven and was only using her as his next victim, it hasn't stopped a group of fans from portraying Eric as just a misunderstood, nice young man who would be cured by having Raven as his girlfriend.
The original Terra gets this as well. Part of it is due to Unfortunate Implications of her being portrayed as sociopathic and promiscuous at her young age to show how "evil" she was (enough to sleep with the middle-aged Deathstroke), while another part is due to some fans holding the idea that she could have been rehabilitated and redeemed of her hate by the Titans. A retcon by Brad Meltzer also cast Terra as a victim of circumstance, driven to insanity by Deathstroke drugging her. Even keeping that in mind, there are fans that will ignore that Terra deliberately murdered Beast Boy's first adoptive father (King Tawaba), and that she was also a dangerous manipulator before she'd even met Deathstroke.
Rorschach gets some of this from the fandom despite being a seriously disturbed hero rather than a villain to begin with, and it doesn't help that it actually is seriously suggested by his canon that he could have turned out differently had his life been better. That doesn't make it any less strange that a short, homely, brutal, canonically smelly vigilante has been made into a cute little innocent tsundere. This tendency was parodied in How Do You See Rorschach?
This also happens to Ozymandias a lot. Due to his noble intentions, there were some people who were willing to rationalize his deeds even after his mass murder