Are...are you even paying attention to what's posted here? I'd wager that 8 times out of 10, what's posted isn't just simple mistakes. It might not be outright malevolence, but the kinds of people presented here are not the kinds who will learn anything whether our actions are kind or not. Most of what I've seen here are like people who bang two rocks together then blame their roommate, who gave them the rocks, when they break. If they refuse to learn, if they prove themselves immune to the very concept of shame (and, let's be honest here, we all feel at least a little shame when we screw up), then posting about them where others can be amused at their blatant, painful ignorance is the best purpose their posts could possibly serve.
Let me give you an example: FSTDT (Fundies Say The Darndest Things) is a site which aggregates publicly-accessible quote from various sites, quotes whose content is either fundamentalist, racist, or conspiracy theorist in nature. Most of these people, like Ray "Banana Man" Comfort, are immune to shame. If they weren't, they'd realize what they're saying is stupid and correct said ignorance. The purpose for which they are originally posted is to preach to the choir, as it were; an action that perpetuates ideals that are, generally speaking, harmful to society. By laughing at them, we defang them. By laughing at them, we show others that what they're saying is complete bunk. Using their quotes as a source of entertainment is also a public service. In the end, we help more than we harm.