Originally Posted by RachelDawes
He wasn't just taking the blame for Dent's death, but for the people Harvey killed. Those crimes couldn't remain unsolved, so Batman just stepped up and said he did it. Batman was already unpopular with quite a few Gothamites so his being tabbed as a murderer wasn't as big a deal as Dent being revealed to be one.
No it was much much worse to exchange the living active symbol of hope and justice for a dead martyr IMO.