It's a team based game, effective communication can help win tough games. With all things held constant, 2 equally matched teams, the one with better communication will be more likely to hold it together for a comeback, press together to win on advantage, have a more enjoyable time winning, and even more enjoyable time losing a close game. There's no denying this, the only argument really left is that the community itself is too childish and toxic to play together.
Childish and toxic players will be who they are regardless of communication type. They will be toxic in both systems and eventually force you to mute (albeit chat is a bit more annoying). There's no real difference there, but in voice at least the toxic person complaining can just speak his peace and move on when he realizes he's been muted. As opposed to the toxic guy typing in his argument while ur base is being razed.
My experience with voice comes from dota games. Sure lots of annoying ppl; music players, foreigners, nasally toxic ragers, nothing mute won't fix. But there are more times than not i'll find 2-3 players that are willing to talk out a strategy and work together. I mean when shit hits the fan and its a landslide loss sure toxicity is high, but game is already lost u can just mute at that point.