not liking someone else's opinion on a certain subject. And I don't consider that a valid reason for you to be able to control what posts someone else can see.

I think for a recip ignore to even be considered there has be a consistent history of personal attacks between two posters, and it has to happen often, not just occasionally. Disagreeing with an opinion is not a reason for a recip ignore, but by all means ignore someone if you dislike their opinion enough that you don't want to see any of their posts. I don't see why this is not enough to take care of the issues the huge majority of the time.