Exactly, because people don't care. If someone insults me? Oh well, it's the internet, it won't ruin my day. No matter what you do there's too many people that play this game you have contact with from others places. In real life it's the same thing, if you throw 8million players in a big area and expose yourself to 9 at of time and expect to do something teamwork based, I guarantee people will blame you. Maybe not out loud, but in there head they will.
The internet gives that anonymity a voice in Dota like it does in everything. You think this doesn't exist just as poorly in other games? There's a million mexican based slurs in Halo. In CoD you're called a little bitch and people message you. Unless you mute every word and only allow communication through the chat wheel (which would kill the game), then this kind of flame will always exist.
As everyone else said, grow a thicker skin. You've been given tools to mute people, use them. It's not going to go away, individual Dota players aren't professional athletes that are going to be held responsible for their words and honestly? I wouldn't want them to. 99% of players are emotional and don't mean it beyond temporarily being mad they lost. The 1% that do and harass you beyond that, you know what you do? Report them, block them, and move on with your life.
I hate to break it to you but - life goes on.