8 Worst Things Two-Face Has Ever Done
4. He Freed The Joker
Batman: Hush came during a somewhat unconventional time for Harvey. He'd undergone reconstructive surgery to have his scarred side erased, and attempted to carve out a new role as an ally to Batman and Gordon. Neither trust Harvey, and though Dent manages to save Bruce from Hush, he also doesn't emerge from the comic untainted.
During the story, Dent actually uses his connections to release the Joker from Arkham Asylum. Given the sheer amount of murder and mayhem the Clown Prince of Crime has gotten up to in his decades spent in Gotham City, that could potentially be considered just about the worst thing Two-Face has ever done. Joker would go onto murder and wreak havoc against Batman, his allies and Gotham and numerous occasions in the years following Hush's conclusion, and though it's always inevitable that Joker will break out of Arkham at some point, it's also true that Dent expedited that process.
If that didn't lessen Dent's role in the book, then the fact he also used his legal expertise to effectively get away with murder (having shot the presumed-dead Hush at the end of the comic) surely will.
Also, the fact this period was so short-lived might just make it so much worse than it already is. Dent goes back to being Two-Face in the years following, and it means Hush's Harvey stands out like a sore thumb.