In The Dark Knight, by Christopher Nolan, 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)?
The final encounter in The Dark Knight makes a few things clear:
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,
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 he and Rachel anyway, whether the means were as convenient as they were or not.