Sliding Scale Of Idealism Versus Cynicism: Fan Works
Oyabun tends to slide up and down the scale but keeps the point of middle on the cynical side. Considering it's a story about Naruto's descent/ascent (depending on the reader) into the Yakuza and criminal underworld with a mess of Gray and Gray Morality, it's to be expected. It becomes jarring to watch the optimistic Naruto slowly becoming a I Did What I Had to Do-type Anti-Hero / Villain Protagonist who is a little disillusioned with the world. He even considers making plans to kill Konohamaru, Sakura, Sasuke and Hinata when they find out he's still alive (he had to fake his death upon joining the Yakuza). He's like Pain minus the God complex.
Shinji and Warhammer 40k and Fairly English Story are both cynical, with heroes that do awful things and who have significant character flaws. However, both have a brighter aspect in that however monstrous the heroes may be, they are dedicated toward making the world a better place and have the strength and skill to do so. In Shinji and Warhammer 40k, this makes it slightly more idealistic than the original. Where Fairly English Story lands in relation to its parent source is...debatable.
Ranma ½ fanfics in particular are known for being more cynical than their source, often playing the more comedic elements straight.
Necaberints Phalanx is an interesting case. It's military sci-fi with a child soldier set in the Gears of Waruniverse and things keep getting worse. The main character has had a terrible life, like everybody else, and he's a going rather insane. It sounds like a complete wad of Dark Fic. It's actually rather cynical for a fic about a video game set in a post-apocalyptic hellhole where the good guys are Fascists. The themes of friendship, love, loyalty, camaraderie, and trust appear often and frequently, without the characters being True Companions, they would have all certainly died by now. It's a realistically idealistic work with cynicism jutting into it.
A good study on the differing ends of the scale occurs in Tiberium Wars. On the one hand, the story is cynical itself, with cruelty, necessary evils, senseless death, and disturbing brutality and violence. This is shown particularly well in a brutal moment where a Nod officer has to execute his own wounded because they'll slow his able-bodied troops down while retreating. On the other hand, the story also shows compassion, loyalty, and friendship are powerful forces that can let leaders command their men successfully and can let the dog soldiers on the ground survive the worst. The idealistic side is shown in a scene where Commander Karrde addressed a unit that had been mauled under his command, asking for volunteers for a dangerous mission. He expects them to refuse or deride him for getting so many of the troops killed, only to have the entire unit volunteer, believing that his command was the only thing that got them out of the battle alive.
Although never idealistic, With Strings Attached has the four gradually move from wide-eyed wonder and genuine heroic tendencies to exhausted cynicism by the end, to the point where they refuse to rescue Lyndess, who saved their lives in the First Movement. Slightly justified in that A) they didn't know if the curse on her had ended when the Dalns gods left, and it would have taken them weeks to get her home if it hadn't; and B) she was a skahs, and they were sick, sick, sick to death of skahs.
Drunkards Walk is generally idealistic. Most of the characters are shown to be (or become) decent people at heart, and it's very difficult to find character who is both truly selfish and not batshit insane.
The Emiya Clan is all over the place on this one, probably due to the different authors that make up the community and the many different stories and crossovers being written. Some stories, focusing on harem antics, family comedy, or the power of friendship are idealistic. Others, focusing on the more traditional Nasuverse angles, wars, and the criminal underworld, are extremely cynical.
Calvin & Hobbes: The Series starts out in the middle, just like the original strip. By Season 2, it's nudged a bit closer to cynicism than the original strip, what with all the snarkers and jerkasses, though most villains are harmless. Cerebus Syndrome nudges it a bit more, and Holographic Retro's death outright bumps it. It's still relatively idealistic, just less so.
Episodes like "Thunderstorm" and "Dark Laughter" definitely fit the cynical side more easily, however.
Game Theory plays itself pretty cynically, with being a deconstruction of the original Magical Girl Lyrical Nanoha though it also shows some of the idealism as well. Notably, while the conflict is essentially a case of Good Versus Good, Nanoha's idealism is actually portrayed as a flaw, as it leads to her siding with Precia, risking billions of lives for the sake of one person.
The thing is it works; the one person is brought back to life without any fatalities.
A in-universe debate is had between Danzo and Naruto in Naruto:Asunder before and after their fight. It should be noted that while Naruto is for idealism he sees the world in White and Gray Morality while Danzo is Black and White Morality.
Perfection Is Overrated is somewhat on the idealistic side. It is emphasized that the world is often harsh and never can be perfect, but it's indicated that people can change for the better, and perhaps so can the world. In the end, The Obsidian Lord, the Usurper and the SUEs are defeated with the Himes managing to work together against the common threat, but the deaths of innocent people through the course of the conflict, as well as the lack of a Reset Button, results in there being more of a Bittersweet Ending than in canon.
Despite its heavy violence and darkness, Sonic X: Dark Chaos lies closer to the middle. Sonic and his friends are still heroes and hold their ideals, even if several of them are traumatized by the things they see. However, the rest of the setting is quite cynical with lots of Gray and Gray Morality.