Riot is like a Public School
A kid gets kicked in his crotch and is getting the shit beat out of him, the one getting beat up throws a push to get the attacker off of him. A third kid tells the attacker to get the hell off of him.
All kids get suspended.
If you defend enough people in Ranked, or defend yourself, you can get falsely reported for verbal enough so that you get a chat restriction. The attackers take you down with them.
Just muting them is like walking away from a kid getting the shit beat out of him. It solves the problem for you, but not for the team mate getting attacked. Riot shouldn't encourage this type of bystander behavior. "just mute and move on." No, if someone is being a douchebag I'm gonna tell them to stop.
I have a 30 game chat restriction because of it. But it was worth it.