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 Toting 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 Batman: 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. It's exaggerated in the New 52, where despite his complete murderous past being intact, he's become a Creator's Pet for Scott Lobdell.
Damian has undergone character development, but some of the fanart draws too much attention to the fact that he is a cute ten-year-old kid and not that he is a former child assassin. He has killed people, and even very nearly killed Tim Drake before becoming Robin.
There are way too many fangirls out there who claim that they want to be Harley Quinn for the Joker, a number that has only grown with the release of The Dark Knight and Suicide Squad (2016). And while there are certainly good reasons to feel sorry for her, she's still a murderer in her own right and very much fixated on the Joker - a fixation which he himself has gone to some efforts to maintain. This ended up with the comic character actually being changed to please the fans — in the New 52 and Rebirth eras (after an attempt to make her even more irredeemably evil went down like a cup of cold sick) she's an Anti-Hero who has largely broken away from the Joker, even if she still has feelings for him that she tries hard to fight off.
This is especially egregious in the Joker's case since he's easily the biggest monster Batman regularly goes up against, has crossed the Moral Event Horizon multiple times, and is a complete sociopath to boot. Despite this many fans are willing to ignore this thanks to his charisma, his intellect, his funny lines and for having a nice suit to boot.
The "Gamer Joker" subculture plays with this, recasting the Joker as a thinly-veiled Author Avatar for a very specific demographic of nerd culture who considers himself a champion of the oppressed (read: gamers) and a rebel against a dysfunctional society typified by Jerk Jock Batman. The entire thing is very clearly a parody of the sort of naive, pretentious, entitled person who would idolize the character... and it's barely an exaggeration of a lot of completely serious images.
Really, Batman's Rogues Gallery gets this treatment (arguably) more then any other Rogues Gallery in comic history. Besides Harley and Joker as previously mentioned other candidates include Poison Ivy, Two-Face, Mister Freeze, really it would be easier to list the members that don't get this treatment. And while many of them are Tragic Villains or Anti-Villains that do show standards from time to time that's ignoring that even the most sympathetic villains (such as the aforementioned Mister Freeze) are often unrepentant murderers who do terrible things for selfish reasons.
In the story "Mad Love," Harley Quinn was obviously believing this in-story about The Joker before her own descent into madness.
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.
Sinestro is an occasional beneficiary of this when writers Running the Asylum try playing up the "enlightened tyrant" angle played to much greater Leather Pants success with Doom above and Magneto below. Still, there are a few readers (and writers) who believe that Sinestro is a Necessarily Evil ruler than the space Hitler Expy that the character has been very unsubtly coded as for most of history. His Ho Yay with Hal Jordan in recent years has not helped matters.
In the New 52 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.
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.
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 apparent 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.
More than a few have gone so far as to claim that, if not for Superman, Luthor would have created a utopia on Earth. This is ignoring the stories that show him pre-Superman as a full-on Corrupt Corporate Executive, or 52, where Superman being depowered for a year led to some of Luthor's worst acts ever. The character of Leo Quintum, a scientist who based revolutionary research on Superman's biology, was even created to counter this argument, showing that if Luthor really did want to advance humanity, Superman certainly wouldn't be stopping him. More than a few stories have even had Superman loudly call out Luthor for this, including "Up, Up, and Away", where after Superman returns to work after 52, he disgustedly gives a "The Reason You Suck" Speech that Luthor had a year to do whatever he wanted and all he did was unearth a Kryptonian warship and try to Take Over the World.
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 quite possibly murdered Beast Boy's first adoptive father (King Tawaba)note Deathstroke mentions that she did it off-panel, but it's never brought up again afterward, and that she was also a dangerous manipulator before she'd even met Deathstroke.
Speaking of Deathstroke, he himself has also had this applied to him by fans. Much of it came because after George Perez left the series, Marv Wolfman himself applied it to Deathstroke, treating him as legitimate Anti-Villain with a code of honor who was just caught in a bad situation and didn't truly want to kill the Titans, allowing him to become an Anti-Hero and friendly ally of theirs even though none of this jived well with his previous characterization from when Perez was still on board, in which he was a ruthless and greedy assassin who would stoop to taking innocent hostages and being psychologically manipulative, who created the whole treachery plan that Terra executed, and who very clearly wanted to kill the Titans since he blamed the Titans for the death of his oldest son rather than take responsibility for it himself. Even after he eventually was turned back into a villain who has done even more terrible things, there are still many fans (and writers) who cling to the idea of him being an honorable and moral person.
Many fans prefer to focus on Cheshire as being the mother to Arsenal's daughter Lian Harper, as well as to focus on the idea that there was some love shared between her and Arsenal when they were in a relationship. This has caused many arguments to spring up about her ability to love her children (including the son she had by Catman in Secret Six). This occurs while said fans tend to downplay or ignore the fact that she gleefully wiped out anentire Middle Eastern countrywith a stolen nuke, that she once purposefully got out of a blackmail arrangement by conceiving a replacement child in case Lian actually was killed off, and that she's generally a sadistic Psycho for Hire with a love of poisoning her enemies. Said arguments are not helped by her backstory including that she was sold into slavery as a child and that the Young Justice TV show gave her more characterization and redeeming qualities.
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 are some people who willing to rationalize his deeds even after his mass murder of millions via psychic squid/Manhattan bomb.
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 quite possibly murdered Beast Boy's first adoptive father (King Tawaba)note , and that she was also a dangerous manipulator before she'd even met Deathstroke.
