I strongly agree with this point.
Some of the biggest learning experiences I've had here have been times when I've come and vented about a certain type. I had had some pretty bad experiences with an INFJ a little while back, and went on a multi-page tear about it. It led to a situation where I had to actually evaluate some of the bullshit I was spewing in the presence of real life people as opposed to some amalgamation of concepts in my head. By the end, I realized that most of what I had posted wasn't reflective of anything real.
That said, I recognize that what I did was unfair and caused needless distress, even if it did result in a teachable moment. If I had to do it again, I would have done more to frame my opinion within the context of my experience. I think what [MENTION=14857]fia[/MENTION] is pointing to as the problem is maybe the only thing that could make these kinds of rants forgivable. If someone says, "Look, my XKCD ex did such and such a thing. How much of their horrible is type-related, and how much of it is just because they were a dirtbag?" I feel people would be much less likely to take it personally even if they shared a type with the ex.
Knowing someone's intended purpose can make a difference. I don't think it's fair, for instance, to lump [MENTION=26674]theforsaken[/MENTION]'s post on offense and Fe with some of the other threads that have popped up as of late, because I got the impression her goal was actually understanding something about extraverted feeling. It doesn't serve anyone to cut off possibly uncomfortable subjects of conversation simply because they're uncomfortable, especially if those participating in the thread can agree on the value of engaging with the subject matter.
Speaking to the OPs point, being disrespectful to other people, or being destructive just because, is an issue. Maybe a way to address this would be to challenge posters on what they're trying to achieve. "Ok, XKCDs are all evil, soul sucking narwhales. Noted. What else were you trying to get out of this conversation? What sort of discussion were you seeking besides validation of what you already think?" Etc.
Just my $.02.