Well it does annoy me, especially once I've typed out an opinion to reply back and then find out I've been blocked. However, I get over it and move on. I try not to let things on the internet make me really angry.
Most of the people who do that are idiots anyway. Makes me wonder how they function in the real world, it's almost impossible to find someone who agrees with you completely on everything, get over yourself already.
I try to stay away from these situations if I am going to block I usually give people right to reply but I have to hold my hand up - I have been peeved off enough to do it once or twice but I try not to now - It is very childish.