I don't get the ignore button. If you don't want to read a post, don't open it!! I am in total agreement with bigvern. Why do you actually need a button to ignore someone?
On the other hand, as long as they do have an ignore feature, you may as well be able to ignore aliases too. however, if they do that, the aliases would have to be ignored independently of the handle. If you ignore a handle and the alias is automatically ignored too, then that would out the alias, and defeat the purpose of an alias! (of course the anti alias people will say "good!" but that is not good.)
As for your idea of the whole thread disappearing, why? Some people might want to ignore a a specific poster, but not ignore everyone who replies. And again, if you don't like a thread, can't you just ignore it on your own??
Also as vern said, what is to stop someone from creating a new alias or a new handle?
I just do't get the ignore button!! Are people that helpless, that they need a button instead of just not opening the damn post???