The best explanation I've found is mental illness. He started posting this stuff on another forum under another username about a year ago, and one of the regulars called him by his real name and shared this link: Dennis Markuze - RationalWiki
It's really a sad story, and highlights the risk...
If he has, he would treat you to anti-atheist spam on Nostradamus, punctuated with Depeche Mode videos and rants against James Randi. AFAIK, he focuses on trolling atheist, humanist, and skeptic forums though, so you may not have been graced with his presence. :shrug:
He is posting again though.