A couple weeks ago, I lost a ranked match. In bot lane, we were doing pretty damn well. But up in top lane, our Rumble was having a difficult time against the enemy Nasus. Our mid laner started making comments like "Bronze Rumble GG" and similar, insulting the Rumble for no good reason. Rumble decided to overreact, and said in /all something to the effect of "Free farm top for Nasus", and abandoned his lane to farm jungle and mid. We lost a winnable game because of this.
As a bystander to this argument, I can't mute it to make it go away. I tried to diffuse, but got ignored. Two assholes couldn't keep it in their pants, and I'm left with the loss.
So fuck yeah, I say chat abuse deserves a punishment. Figure out a way to play effectively with your team, or fuck off to a different game. If you can't handle losing without screaming at somebody, stick to single player games.