I think you might be misunderstanding the problem, it's not about disagreement, it's about a bullish refusal to admit that there might be any other perspective to a problem. It's not the disagreement that is the problem, it's the lack of respect for other posters.
I dislike that as well Ė a poster will get irritated because the OP doesnít just automatically change their minds upon reading responses that they donít agree with. Comments like that just arenít helpful at all and lead the discussion into a downward spiral of snarkiness.
I don't think anyone expects or wants everyone to agree, or that every thread has to reach a consensus. That'd be boring. But I can think of a few times when the OP was behaving tantamount to sticking fingers in ears and yelling LALALALAICAN'THEARYOU, and that's childish and annoying.
It's perfectly possible to acknowledge other viewpoints as valid, even if the OP doesn't agree, and it's useful to forestall the thread snowballing. How many times have we all seen dogpiling occur when the OP refused to answer a seemingly simple question? As painful and/or distasteful as it may be to acknowledge an opposing viewpoint, it's the mature thing to do.
(Of course, sometimes when OP doesn't agree with an opposing viewpoint they get accused of not getting it, but that's a whoooole 'nother issue.)