Even though the blocking option is useful, I think that there are some very stupid people out there that tend to abuse it. It goes beyond blocking someone for harassment and you can get blocked just for having a different opinion.
I got blocked by an angry 12 year old just because I don't like the Instagram app and said that it doesn't make you a pro photographer. I didn't do anything wrong, she just didn't like my opinion.
Other people get blocked for saying they hate a certain show or book or pairing, you name it. WOW, I did NOT know that hating SasuSaku or IchiHime was a crime against humanity as a whole. Might as well press charges.
Because of this, the blocking option should only be used if you can select a reason. None of the reasons equate to "not agreeing that my favorite show is the best thing since sliced bread". I GUESS they might say "harassment" or something, but there would be no good evidence of harassment.
Look children, if you see something that you don't like, just wipe the damn tears from your eyes and leave the internet for a while. The internet is FULL of opinions, and many of them are (OH NOES) DIFFERENT! You clearly can't handle this, so go do something useful instead of crying over people's views. It's not that hard.