League of legends, after all, is a team based game. Communication would make the game more fun and strategic. You could coordinate splitpushes, objectives, team fights, ganks, etc . . .
Before someone says it would make league less toxic -
. Many other competitive games already have vc (OW/CSGO),
. People are less toxic in VC than in chat. Behind that toxic, flamer, is a 9 yo squeaker who doesn't want to embarrass himself.
. You could always mute someone / leave vc.
**It is something that can be optional. It will greatly benefit those who want it, and do no harm to those who do not.**
At least, you could make it so only people with a certain honor level can use it.
EDIT: a lot of people are downvoting this for whatever reason. Let me reiterate: VOICE CHAT IS OPTIONAL. If you get upset over a person insulting you, then maybe voice chat isn't for you and you could disable it.