"Someone disagrees with you, attack the poster personally." True enough, that's one way people avoid dealing with some awkward point the other party has made. Another way is to complain about the personal attack, and avoid the point the way.

What we should be tring to do, of course, is to tackle the awkward points head on, and either explain why they are invalid, or accept them, and adjust our overall argument to take them into account. But that would mean we would be engaged in a discussion trying to get closer to the truth, rather than just trying to win points in an argument.