The movie Jokers are more "watered down" so I get it. But comics Joker is such a disgusting piece of filth that I never got the love for him. Joker in most adaptations is kind of a wacky gangster with flair, or an edgy underdog like you said, so again, I get the appeal. Someone like Ledger's Joker was cruel but at least had a specific plan. But the real Joker, the character that he's turned to in the last couple of decades at least, is such an abominable character that I cannot bring myself to like him. Technically characters like Apocalypse, Sinestro and so on have much bigger bodycounts, but I suppose the fact that they have an ideology and an attachment to the wider population, makes them more likeable characters to me. Characters like the Joker for me exist just to get piled on by the hero; period. In the comics he's a pure monster and nothing more. The lack of "fantastical" elements and the similarity to actual IRL serial killers just makes him especially reviled to me.Most versions of the character are mysterious, charismatic, humorous, cool looking, have larger than life personalities, and are usually good antagonists for Batman. It's also the kind of role that allows actors to put their own spin on it. Each new iteration gets a new coat of paint, literally and figuratively, so that also creates interest. As for the comics, most people don't read them, they just know the character from the movies or animated shows. I think the comics Joker is far more sadistic and unlikable than any movie version, which makes him a less likable character.
However, there's another reason the movie Jokers are usually likable, despite being villains. They're not bullies and they are usually in a somewhat of an underdog position. It's the same thing they did with Hanibal Lecter in Silence of the Lambs. Sure, Hannibal is cannibal, but he's also a trapped animal, in a prison that's run by an even more unlikable slimy character. This guy has Hannibal under his thumb the whole film, so it puts Hannibal in a better light, to the point it makes the viewer take Hannibal's side at times. He's got admirable qualities too, which makes you respect him, unlike the other bad guys in the film.
The Joker is usually not depicted as a bully or in a position of complete power, at least not initially. Jack Joker was a criminal, working for an unlikable boss. That same boss tried to have him killed. It instantly puts Jack in somewhat of an underdog position. Jack Joker also stood up to the other crime families and killed several of the top bosses that weren't very likable. Same with Ledger, not in a position of power, and like Jack, he had to take down the mob, which were a bunch of unlikable characters. If anything, he did more for Gotham than Batman with his no killing code. And Arthur, he's the ultimate underdog, and the people he killed, you as the viewer, kind of want to see them get killed by Arthur, as terrible as that sounds.
I think those are some of the reason Joker is popular. I just think he looks cool and does cool villain ****, but never in a way it makes you hate him, at least in the movies. I'll say this, it was satisfying to watch Batman beat the **** out of Jack, because he could be a real prick, and knowing he was responsible for killing Bruce's parents, that made him somewhat unlikable, so I was really rooting for Batman. But then Joker puts on the glasses and starts making lame jokes and dancing around until he dies, and I can't hate him. Jack's personality wins me right back.Ledger was similar, but at no point did I hate him. It was satisfying to see him fail at the end when the people did not blow up the ships, and he's looking at the clock and gets pissed off, that was not only funny, but really enjoyable. The cruelest thing Arthur did in the film was probably locking the door and laughing at the little guy when he couldn't reach the lock. That was funny, but incredibly terrible. But then Arthur lets him go and gives him a kiss, so there's always something to counterbalance his villainous acts.
Entertainment has a way of glorifying criminals and scum. We're all guilty of liking some of these characters. The Bounty Hunter, the Gangster, the Mastermind, and so on. People all over the world are in infatuated with the Peaky Fokin Blindahs, and they're trash human beings who promote a slew of destructive behaviour. But they've got enough understandable qualities to make them stand out for serial killers. They're a family, they take care of their people, they want to go legit, they ultimately just want their piece of the piece. Meanwhile characters like Carnage are just petty and cruel killing machines. Joker is the prime example of the "realistic" and "it could happen to you" villain so I cannot seperate my disgust from the character. I find it enjoyable when Batman gives him a "you will forgotten" speech, and it always irks me when his "ideology" survives in some AU futures. I want to see him fail. As for the "ultimate Bat-Villain", he works as an antithesis, but I've always found him a contrived nuisance, and preferred Ras and Bane as his actual nemesis.
Nicholson Joker, Hammil Joker, Ledger Joker, Phoenix Joker, those are all enjoyable acts. But comic Joker? Pure ugliness distilled in a single character.
