There are, unfortunately, lots of posters on the Dis who think that being childless invalidates your opinion on many topics. I am kind of shocked that you aren't allowed to have an opinion on which park might be more enjoyable for kids, though. So silly.
I read the threads, too. Posters moved from offering opinions and counterarguments to ad hom attacks and straw-man arguments, among others.
Unfortunately, some people participate in those kinds of logial fallacies when they can't counter the ideas or opinions. I don't know why, maybe they feel it gives them more credibility? Anyway, it never really does anything except alienate people, and I'd think that's the last thing we want to do on the DIS.
To the OP: This does happen on the DIS, as it does on other boards, and more than we perhaps like to think. It happens if you're willing to take a stance on something--it doesn't matter if it's politics, religions, taking kids out of school to go to Disney....or if you prefer spinach over iceberg lettuce. I almost think it's the nature of the forum.
Just remember, their responses aren't about you; they're about them. Responses like that are about how they feel the need to defend their ideas (territory, values, expertise, whatever). Or they're about the need to validate their positions. Or they're about the posters feeling threatened by counter-arguments. Or they're about feeling vulnerable because their positions are in the minority and so they respond aggressively. Or whatever.
What's important for you to know is that you can't control how people respond to your posts. Or even, to some extent, your initial reactions. What you can do is control your reactions. In many threads I read posts that say, "Don't feed the trolls." Although we might need a specific name for such posters--the "ad hoccers"?--I would say similar advice applies.
ETA: For those who are interested, I looked for a term for such posts on this site:
http://redwing.hutman.net/~mreed/