A loyal fanbase is the motherlode of any writer or producer of fiction. But it has side effects. One of them is the tendency of a given fandom to bash another. But this is more than just Fandom Rivalry.
Fans of a given work have a unique ability to recognize all the failings of a rival franchise, and yet completely miss that their favorite franchise is guilty of many of the same shortcomings. This also works the other way around: Sometimes fans will hold up a work as a masterpiece, and miss the fact that many of their favorite franchise's qualities are also present in the works they despise.
This becomes all the more ridiculous when you'd think both franchises would appeal to the same audience. Of all types of fans, maybe this type has the most similarities with supporters of teams in professional sports (Football, Baseball, Soccer, etc): They enjoy the same thing, but have to take a side.
Quite often fans will accept the flaws with their own franchise, but will dismiss them as too minor to count, not important, or even as totally separate (for example non-canon). At the same time they will make a big thing out of equally minor and unimportant flaws in rival franchises, or even parts that are equally non-canon. A classic example is "well, you can't expect a series that long to not have one or two bad episodes", vs constantly referring to the bad episodes or parts of them when attacking rivals. Bad effects, goofs etc are not important in your own favorite, but give endless ammunition for attacking the rivals. This applies to sports too, where that humiliating defeat your own team suffers is ignored or excused (bad luck, bad ref etc), whilst anything that even comes close in terms of a rival team will be the ultimate proof of just how much they suck.
This phenomenon can also occur within a single work without getting Fandom Rivalry involved. A basic example is characters with similar backstories or personalities who invoke completely different reactions from the fandom. For example, the resident Draco in Leather Pants and Scrappy of the fandom might both be orphans who became Punch Clock Villains for the Big Bad to survive, yet the fandom thinks one is being exploited by the Big Bad while the other is supposedly an irredeemable monster for helping them out, despite the fact that both of them helped the Big Bad.
This also is not limited to Fandom, Hatedoms can be just as hypocritical (In fact, much of this kind of hypocrisy tends to come from a show's hatedom). You have those people who hate on stuff because they don't want to be seen as some mindless bandwagoneer, whilst ignoring that they're jumping on the bandwagon of hating it.
A subtrope of Fandom Rivalry and Hypocrite. Vocal Minority is where most of this comes from. Not So Different is often invoked. If the fandom is called out on the hypocrisy, the No True Scotsman fallacy can sometimes be invoked to deny that their favorite works have what they are criticizing.
Tropes which rely on, or include this fallacy:
- Acceptable Targets
- Cultural Posturing
- Console Wars
- Computer Wars
- Double Standard
- Even Nerds Have Standards
- Fandom Heresy
- Fan Dumb
- Fan Hater
- Franchise Original Sin
- Hate Dumb
- It's Popular, Now It Sucks!
- Nostalgia Filter
- Outgrown Such Silly Superstitions
- Public Medium Ignorance
- Selective Obliviousness
- Unpleasable Fanbase
- The Tropeless Tale