One of the characteristic, unreasonable debating tactics deployed by some of the more virulent 4E bashers has been to switch freely between emotive feeling and argument, and then whichever way they are answered, to switch to the other. As to why, I could make several guesses, but I don't think that would be wise, except to say that many reasons why are a lot more benign than one would first think. And from the receiving end, it really doesn't matter why. If it happens enough, you feel rather annoyed. See, we have feelings too.
Great post! I was relatively new here a few months ago and got ensared in several "version" debates. Honestly, I can't say whether I was being "emotive" or "logical", however I'm sure I might have appeared emotive more than a few times simply because I was new to the board, had not seen what a pervasive issue this whole thing was, and probably reacted pretty incredulously to the entrenched attitudes that have developed around the whole thing.
I'm a 2e / 3e player and mostly would like to stick to discussing those versions. However, I see a lot of value in some of the 4e approaches even though I don't want to play that version. So originally I felt discussing all flavors of DnD just seemed to be the thing to do. Looking for common ground with other players over what they disliked and liked about each version. Sadly, it just can't be that simple.
I'm a fan and critic of all versions I suppose. I'm even a fan of a good debate. I'm even someone who is a bit more intuitive/emotive maybe more than logical (more storyteller and less mathematician) so I can give people leeway for getting defensive or too offensive. I also try to make it clear when I am giving an opinion based on just what I like about an RPG as opposed to some objective measure (and it's funny how often people want to argue about that.) What I can't give people leeway for is dragging me into an unproductive argument.

Lot's of times people think a debate means you pick a position and cling to it come hell or high water. That's when feelings get hurt IMO. They forget that sometimes people lose, sometimes people win, and both sides need to be paying attention cause they should both learn something new and useful in the end.