Sun Tzu would tell you (your son), to avoid playing to his enemy's strengths. In other words, don't engage them in a forum where one needs to be quick-witted. An on-line chatroom, or a blog is a terrible place to engage in a debate, because so many of them "pile on." Even if your son understands the arguments, and has facts on his side, it's useless if he can't have a forum in which to make a rebuttal.
I tell him that. He gets in debates at school. And since he gets frustrated and can’t make his point they all pile on...they do it just to have fun watching him get spun up. I know their type...I’m one of them. I am always getting people spun up just to see their reaction. So I know exactly what my son needs to do to diffuse it and not feed them, but he wants to be like me in debates so it’s easier said then done for him.