Basically, I only consider something "ad hominem" if the flaws pointed out are irrelevant to what is being said. I think background is relevant when someone is

Basically, I only consider something "ad hominem" if the flaws pointed out are irrelevant to what is being said. I think background is relevant when someone is presenting something as a fact that may not be (like the statistics in this post). When background is irrelevant is when it's used as an attack on someone's logic. Even if it's Stalin saying "Murder is wrong, because kills someone", it doesn't matter that he himself was a mass murderer. It would make him a hypocrite, and a terrible person, but his logic still stands by himself. On an unrelated note, I liked your (unintentional?) subtle humor of pointing out who wrote the article on ad hominem.