Today it seems that not liking someone is an accepted reason for prosecution.
John Edwards had two main things against him: he acted like a scumbag to his former wife, who was a very sympathetic woman; and he was a partisan politician during the reign of another party. That seemed to be enough. Not only was he charged with numerous offences that were widely known to be trumped up, but there was very little public outcry.
I don't want to repeat the whole sad story, but there's a good analysis of it here: John Edwards case was once thought too sensitive, Justice official says and Government failed to prove case in Edwards trial, jurors say.
For the people behind the prosecution it was win/win: even without a conviction, Edwards' dirty laundry has been so thoroughly aired that not only is his career unrecoverable, but his party's reputation is tarnished as well.
It's easy to call for justice in cases like that of Aung San Suu Kyi, the Burmese politician and winner of a Nobel Peace Prize who was detained for decades by a military junta. It's not so easy to stand up for someone like John Edwards, who is thoroughly unlikable. The big story in the John Edwards case is not that he cheated on his dying wife, but that he was a victim of malicious and politically-motivated prosecution.