A thumb down is not a vote... it is a public slap (a weak one, again I am more amused then troubled by this, but it is a slap nonetheless).
There is the "hide" aspect of it, but I don't really think that anyone cares about hiding posts (threads sure, but not posts)... you don't generally go back and read old posts anyway, so hiding them doesn't help at all.
The real reason for the thumb-down is to offer a (albeit weak) symbol of disdain.
I don't like the idea of an anonymous show of disdain. I would prefer names to be attached (again, this is amusing, but not a big deal).
The ignore feature works the other way-- there is counter on how many people have me on ignore. It's main purpose is not to show disdain, in fact I don't think there is a way for me, or anyone, to know how many people are ignoring me.
But, here is a real peeve (this one actually bothers me a bit). The ignore feature is supposed to be anonymous, yet there are constant broadcasts of who people are ignoring. This takes what is a useful anonymous tool and turns it into a public shaming.
The public ignore is petty and boorish.