It's melodramatic and it's somewhat powerful that someone would do that for a friend, but in the longterm, that simply doesn't serve Gotham's interests. A truth built on lies is...eh, someone get Jonah Nolan to finish that for me.
It's not in character in relation to the comic book Batman in the least. Batman, in his dealings with people, expects them to take responsibility for their actions. He always has. He may believe they are redeemable, and look for the good in everyone, but he's not one to sugarcoat the way things are. He is not someone who goes "Harvey, I will totally bail you out because you turned to evil and betrayed the law".
The whole point, what makes Harvey Dent's "fall" so powerful is that this man who was one of Gotham's champions becomes one of Gotham's greatest enemies. Not that he is redeemed through lies. It's not in character, it's not faithful to the mythology, and it doesn't honor the mythology and Dent's place in it, either.
Gotham isn't going to suddenly become a horrible place with Dent gone. 500 of it's top criminals are locked up with easy charges to be brought against them.
I'm not interested in looking at how Gotham would react in realation to how they view Batman (Not all of Gotham will react the same, which makes this plot point harder to swallow). I'm interested in wondering why the hell Batman is so eager to accept the blame for other people's evil acts. He wouldn't. No version of Batman that I've ever seen would.
Obviously Dent WASN"T the best hope Gotham to offer, and trying to LIE to the city and make it look like he was is absurd. Look what he succumbed to. Nevermind the absolutely absurdity of the police not hunting Batman until he supposedly kills MOBSTERS. Not innocents, mind you, but MOBSTERS. People that prey on the innocent, who almos anyone in Gotham would care less about.
This angle didn't need to exist for Batman to be on the run. And frankly, it would have been far more powerful if Dent's image wasn't "saved" through lies and deceit. That's going to come back to bite them in the ass at some point.
-I agree with some of your points BUT
Another reason to why he took the blame is to make the criminals truely fear him, as Maroni told him, I don’t remember the exact line but that the criminals are not afraid of him he has his one rule, he doesn’t kill.
I’m not saying this is makes up for all the mistakes involved in this move, but its another motive for him to take the blame.
I think this part of the story will be over in 10mins or less in the next film, so it doesn’t bother me much.
It’s not like the film is being 1000% truthful to its roots, and its not like it matters enough to ruin the film experience.
Taking the blame for the murders enhances the film IMO but takes away from the character so I think it was the right move. It enhances the film because
A- Bats thinks maybe it wasn’t Harvey’s fault he was driven to madness-if you want to call it that, and he sympathizes with his quest for revenge as they both cared for the same person and they both have been in a similar position.
B-Bats wants to strike fear in the criminals of Gotham, he pretty much looses the power he had from the first film in this one, this is a weird way but still a way to get some of it back.
C- Bruce respects what he did for the citizens of gotham and he wants them to believe that others can come along and do the same. By keeping his reputation clean, more citizens will want somebody as good as dent and hopefully will vote that characteristic in.
D- Maybe some citizens will respect him more because he’s not afraid to actually kill some bad guys, he already gets a mixed reaction from gothams citizens so what’s really changing besides the cops chasing him.
It takes away from the character and somewhat from the logic of the character for the reasons you’ve previously stated.
Regardless there are many interpretations to this move, by no means is it enough to hinder the film experience IMO, not saying that it did that for you but in general.