Just for the record, since some people apparently aren't clear on this:
An ad-hominem attack is when I claim your argument is wrong on the basis of some element of your character. It is NOT when I claim a flaw in your character on the basis of your arguments.
If I say "You are idiot, therefore I'm not going to respond to your evidence or arguments", that's an ad-hominem attack.
If I say "Due to your complete lack of presenting any evidence or argument, I must conclude that you are a blithering idiot", that's just an insult.