Re: Why respond to this guy?
Same reason I respond to committed leftists over on the political channel. I know I'm not going to convince them until Hell freezes over, but explaining the flaws in their thinking might inform a lot of other people looking at the posts who might not have otherwise considered the issue at all, and if there was no response, might see only the original post as the extent of the information available.
Or in short, like Tron, I fight for the users, or to be more specific, the lurkers.
Besides, it's fun.