I just leave the thread without comment. And the reason has to do with "let's agree to disagree". This sounds perfectly reasonable, but it seems in many cases, people say it *after* they've just rebutted something. So to me, it's no different than if you started your post by saying "I need to rebut what you just said, but then I'm checking out".
That's why I just stop posting in the thread. There's a risk, I guess, that it looks like I walked away in the middle or I'm avoiding a question, and that's certainly not how I behave IRL. In fact, I own the last word! But in this forum, if I've said all I have to say, I just take that risk.