It's well documented that he's creep in real life. Nine women, including minors, have accused him of inappropriate behavior. His co-stars have had problems with him too. He apparently took the Joker character a little too seriously.
I don't particularly like Leto, but I think the bigger issue here is that its insane to have put a quarter billion in production and a hundred million into promotion of a Tron movie given the history of the franchise.