“The problem is that what the questioner thinks is relevant and what the answerers think is relevant are not always the same thing. If a question is loaded with presuppositions, anyone answering it is quite right to question those presuppositions before (or rather than) answering it.”
I run into this one all the time, most recently in a discussion about how society felt about emerging technology affecting privacy, but the OP cared ONLY about “creeps” taking pictures yet did not want to discuss even the as-asked question. Most of the thread turned into me being told I am wrong, nothing I have to say has anything to do with anything, they are right, and anybody who disagrees is a horrible human being.
Given how many times I have seen someone who has a viewpoint that differs either from a precious poster or from the OP’s agenda turn a thread into nothing but a 2-person argument that makes everyone else wander off in disinterest, I’d say the filibuster happens quite a bit.
That said, I don’t think it’s intentional. I think it’s most often because there are some people that are too closed-minded to ever do something such as agree to disagree, and some people so misinformed (and proud of it!) that they are just a lightning rod for vain attempts at education. Trying to convince people that the Earth is round and the sky is blue despite what Fox News says can derail a thread pretty quickly. But it’s not an unwritten protocol any more than “water seeks it’s own level”; it’s just a natural occurrence.