I don't think muting should be an option.
I think that allowing people to mute other people just allows for the deconstruction of teamwork. Even though the feature is for muting toxic people I've only seen it be used by toxic players whenever their slightly under-preforming teammates try to explain their actions. If you can't her the rest of the team, you can only communicate by pings. If you can only communicate by pings, more complicated strategies become nearly impossible. IF you can't execute complicated strategies, you can't win. Riot is pretty much allowing toxic players to leave their teams to die.