I am not a downvoter, but using your own analogy, your post is like saying "Why are people complaining about the existence of minefields?", criticising people for suggesting that something should be done about the minefields and ignoring the fact that the victims of minefields are mostly people who didn't know there was a minefield there.
Also, I think in plenty of these cases the victims are not going to the places where their attackers are. E.g. the victims of attacks organised at 4chan are not generally people who post on 4chan.
I would say that blogging on the internet is more like going out for a drink at the pub. You aim to meet and interact with many people with the same interests, have discussions, and enjoy a drink.
However, there is the possibility that someone may abuse this, maybe through drinking to excess and becoming argumentative. This, while annoying, can be accepted. However, if that person gets violent and causes harm, I believe that is unacceptable.
