In our standards of discourse, we don't seem to have a good way to say "I disagree with you on points X, Y, and Z, but I also don't consider them that relevant to the broader context", or "I disagree with you on point W, but it's getting off-topic". I'm not sure if this is a good thing or a bad thing. Fairly often I see people dropping a trail of things that are both irrelevant and wrong in discussions, and if I point out that they're wrong, we're suddenly in a long discussion on that something else.
There's this general expectation among well-behaved debators that they can generally back up what they say, and this tendency that if our statements are challenged, we will do our best to defend them; result: easy derailment. Other result: intentional derailment.