He's not been derailed. I've always considered Jason to be evil from the time he was retconned into his current origin. He was just being watched too closely when he was Robin to really get away with much, yet he still managed to push a guy off a ledge and other stuff. Once that leash came off, though, we see his true colors: he's a thug, a murderer and a sadist who likes to dress up his wallowing in his basest instincts as 'justice' or 'going the extra mile' when all that really is is behavior just as sick and criminal as anything the Joker does.
Really, anyone that gets behind the 'yeah, some people just deserve killin' without a trial or any of that pussy stuff' deserve to be reviled. I think it would have been better for Daniel to come out and say 'you guys know Jason is and always has been a /bad guy/, right? Right?'.