What's the problem with answering them? If you know they're perverted, just don't bother with it! This site is for 13+ for a reason you know, we can say pretty much whatever we want.
I wish people would. But some say that it's "fun" to do so, or that "someone has to" but my thoughts are "um, no you don't, no one is forcing you too, and if we hate him so much and answering him isn't making him go away, so either we like his presence or we're not mature enough to walk away."