It's pretty much exactly what it looks like, pleasure in the bad ass motherfucker living up to his name and kicking ass while being a real motherfucker. That's why the Joker becomes a secondary hero.
The real Batman/Joker confrontation, at the skyscraper, becomes anticlimactic. The interview scene falsifies the outcome. The same Batman in the interview room would have killed the Joker. A lot of all this is simply groupthink---at some level, people are thinking, we (the US) have to be ruthless to rule the world. So they want to daydream about heroes who can be what the times demand. The Joker in the interview room represents a fantasy about the triumph of the will.
Does anyone really think that Batman reproving Dent for trying to brutalize one of the Joker's minions is a dramatic irony? It's a foreshadowing of Dent's total failure, which is the failure of law and democracy, redeemed only by Batman's noble sacrifice. Except that the real climax of the Batman story was unintentionally funny. That is one reason why Dark Knight Returns just isn't all that good. Part of what made this movie more watchable than Batman Begins was that there were two storylines. Neither were very good but switching back and forth simulated drama.
The intersection of the two plots was in the Joker/Dent confrontation. All that ostentatious foolishness about Batman and Joker being the same misled viewers who enjoyed the cruelty and wanted Batman and Joker to be the same. It was Dent and Wayne/Batman who were the same. So, the confrontation between Dent and Joker had all the thematic weight of the film. Nolan's Batman pretty much is just a dumb thug and of no adult interest at all. The problem for Dark Knight Returns fans is that the scene is deeply weird---not very convincing dramatically with no feeling of truth whatsoever.