Why voice comms would reduce Toxicity overall
Since this was instantly deleted on reddit for unknown reasons (if it's something to do with the content of my post rather than the idea please let me know, I'm unfamiliar with what gets a post removed)
TLDR; Lengthy post about a few key points of why voice comms would reduce toxicity rather than cause it. Tone/audience/misinterpretation
Contrary to Riot Lyte's beliefs, I think voice communication would prevent more toxicity than it would cause. Anytime I can get the team I get matched up with on Curse voice or teamspeak, I remember those games as a hell of a lot more fun/exciting than the silence of text followed by spam pings and "muted" "reported".
First, things that aren't meant to be toxic and are being misread with the wrong inflection by the other player would be clear by the tone of your voice. Similar to how when people use punctuation in a text message you assume they're being short with you by abruptly ending the text, an open sentence with no punctuation however means the conversation is still "open". I believe people with a natural habit of swearing or being profane quite a bit are being punished for statements that may be quite normal for them, merely because an excited statement of "Get fuckin baron!" is misconstrued to be something negative.
Second, less people would get frustrated about someone not doing something, because its hella hard to type to your mid laner to come down river when he's zoned out (mentally)/tunnel visioned csing, while you're being chased by 3 people towards him. This would eliminate the post death rage because NO MIA WTF RETARD. You would be able to relay what you need and where you need it in a much faster manner.
Third, you immediately get a sense of the age group you're speaking with in the game and can adjust your language appropriately. This whole thing obviously could be abused as any system can be, cough the current report system cough, but I expect you to see a drastic drop in reports and toxic behavior and only the most severe cases of toxicity remaining. Which then could easily be taken care of at a much faster rate, purely based on the lower volume of reports received.
Considering a majority of the playerbase probably plays other games and have never been banned or "punished" (I think punished a Riot only thing) in any of them, it's clearly a flaw somewhere in your system or player management rather than the players themselves.