It happens on any board. Sometimes you will get someone that is intolerant of others' viewpoints. Rarely, it is an atheist that does not accept any possibility that there could be a God, good or evil. More frequently, you get Christians that insist that anyone that doesn't believe in God or that Hates Him is damned. Sometimes you even get active witlesses, or people that think like active witlesses, trying to "save" people that have "gone astray". General trolls also appear on any forum.
But, from what I have seen here, the posters that are like that are in the minority. Most people attack the post, usually finding holes in the reasoning, instead of the poster. I personally find those people that post extreme viewpoints or predictions as useful as those who are more moderate--what is extreme or implausible now could well become practice among the witlesses in a year or two.