I have this problem quite often. For some reason, I find it difficult to allow some arguments to go uncontested. They tend to be the really stupid ones that I feel have simple answers. What I don't often realize is that the people making them are doing so because they're ignorant and are really bad at arguing. The problem with those people is that they don't know they're bad at it, so they'll keep arguing for as long as I will. They also don't know they're ignorant, so they'll continue to not listen to me and refuse to be educated.
Of course, that's how I see it. They probably just think I'm an idiot who won't shut up.