I'm sorry to say that, but you're enough people in staff to manage banning new accounts from him. There's no need to give up at all, because this shows that he won over the staff and the whole amount of people not wanting him here anymore. He's one single guy, c'mon.
Yes, first step: don't give negativity any room in here by deleting those posts asap, before they trigger more people. Or y'know, just ban him. Next time, I'll just use the "report post" option, then. Feel free to move my rant away from this topic then, but I definitely won't give up this cause.