Why didn't Batman tell Harvey Dent that he tried to rescue Rachel?

Question

In The Dark Knight by Christopher Nolan, Harvey Dent blames Batman and Gordon for the death of Rachel.

Harvey: The world is cruel. And the only morality in a cruel world is chance. Unbiased. Unprejudiced. Fair. His son's got the same chance she had: fifty-fifty.

Batman: What happened to Rachel wasn't chance. We decided to act. We three.

Harvey: Then why was it me who was the only one who lost everything?

...

Batman: You're the one pointing the gun, Harvey. So point it at the people responsible.

Harvey: Fair enough. You first.

Why doesn't Batman just tell Harvey Dent that he tried to rescue Rachel, but he failed because the Joker lied to him? And, would that have changed any of Harvey's actions or would he have still been rampaging (sort of)?

Answer 1

The final encounter in The Dark Knight makes a few things clear:

1. Dent views Batman's responsibility for Rachel's death in a markedly different light than Gordon's responsibility. His discourse with Gordon (before Batman shows up, after Batman is shot) is full of authority and disdain, while his discourse with Batman is less sure and contains more attempt at justification. Along those same lines,

2. Dent ultimately does not blame Rachel's death on a lack of action (or a poor decision) in the rescue attempts; he blames Gordon's staffing choices. Throughout the movie, he makes references to not liking Gordon's unit (MCU), which is "full of cops [he] investigated at Internal Affairs". He talks about "scum like Wertz and Ramirez", whom Gordon should never have trusted (and who were the specific cops who picked up and delivered Dent and Rachel).

And so Dent punishes (shoots) Batman because Batman claims responsibility, and Dent as Two Face is a bit of a madman. But Dent attempts to punish Gordon because he ascribes responsiblity to Gordon. And on some level, he is right--Gordon had dirty cops working for him. The thing Dent missed is that the Joker would likely have gotten him and Rachel anyway, whether the means were as convenient as they were or not.

Answer 2

Because Batman does feel responsible for Rachel's death

Batman may have chosen to go and save Rachel after the interrogation, but that doesn't mean that he put his responsibilities "at ease" when he found out later, that the Joker had lied to him.

In the passage you included, this is clearly stated:

Harvey: The world is cruel. And the only morality in a cruel world, is chance. Unbiased. Unprejudiced. Fair. Your boy has the same chances she had; fifty-fifty.

Batman: What happened to Rachel wasn't chance. We decided to act. We three.

Harvey: So why it was me the only one who lost everything?

Batman: It wasn't.

He doesn't point out that the Joker had switched the location to trick them, because this had little to do with the ultimate situation. Batman thinks that by allowing Joker to thrive, he let Rachel die and Harvey Dent fall. Although the death as an event was totally on Joker, the death as the outcome was one way or another, on Batman (from his perspective).

Alfred: I prepared a little breakfast.

Nothing. Alfred sets down the tray. The envelope is propped against the silver teapot.

Alfred: Very well.

Wayne: Alfred?

Alfred: Yes, Master Wayne?

Wayne: Did I bring this on us? On her? I thought I would inspire good, not madness-

And later on:

Alfred: Gotham needs you.

Wayne: Gotham needs its hero. And I let the Joker blow him half to hell.

Alfred: Which is why for now, they'll have to make do with you.

If the Joker had not lied, wouldn't Rachel be alive? Possibly. But his reasoning is way more complex than that. Batman feels the burden, that as Gotham's dark knight, he had to prevent all these tragedies way before, than just act at the last minute, waiting for the situation to unfold by itself.

Let's not overlook the fact that the abduction of Harvey and Rachel, happened right after the press-conference where Bruce did not find the strength to come front and admit that he was the Batman, either before or after Harvey falsely claimed that he was.

Had he admitted it, none of these would had happened (at least, in his own mind).

Answer 3

Because it wouldn't have changed anything.

Harvey: The world is cruel. And the only morality in a cruel world, is chance. Unbiased. Unprejudiced. Fair. Your boy has the same chances she had; fifty-fifty.

In Dent's mind, there's a fifty percent chance that Rachel would have lived. Ask yourself, does a truthful Joker really alter that chance? Considering that the most important variables in getting to Rachel in time are

1. When Batman and Gordon find out about the bomb.
2. How far away the pair of them are.
3. How much time is left on the bomb.

None of these are dependent on who is at which location. To us, the viewer, it seems obvious that Batman saves whoever he finds, but to Dent, he must assume that the GCPD, if corrupt, is at least as qualified to drag someone away from a bomb as a man dressed as a bat.

In short, the Joker lying about the location shouldn't, at least to Dent, have mattered. This is because, even though we as the viewer know different, Batman and GCPD should be equally qualified at saving either Dent or Rachel.