With the new ping system you can tell your team mates most of the important things without chat. Chat is mostly used for harassing and flaming.
Muting someone is an option, but it still does not prevent them to type and tilt other team mates. They also don't know you muted them.
I propose a following feature: **option to disable the chat completely**. With a clear indication on loading/score screen that the player has chat disabled (and flaming him has no point). I'd also go as far as disabling chat completely for some games (for all the players), but that could be a next step.