What do you think is the cause for toxicity?
In my opinion, the cause for toxicity starts from a player that has a terrible game. For example, Player A is on tilt, begins flaming someone and eventually Player B will be responding and both players will be arguing with each other. Game over, next game Player A and B will be flaming someone else.
There are options where you're stuck with a premade 4 and they just begin bashing you because you're not in their premade and you can't do anything about it except take it because you're most likely going to get reported by all 4 of them and have a higher chance of getting punished regardless of what you said because a report is a report.
Thirdly, you have players that are intentionally feeding or afk and refuse to cooperate with the team. You can try motivating them to play but then they start bashing you which leads to reason 1 earlier.
Any ideas on how to drastically reduce toxicity?
How you can fix this is you send the entire team chat log and review it instead of just reviewing the player that is reported' chat logs. Like for example if I am responding to someone who is sending me death threats or spamming me pings, I shouldn't really be punished even though the mute button is right there. If you're getting verbal abused, why can't you respond to them? Yes it makes it worse, but my entire day is ruined already just cause I have been bashed on so what's wrong if I respond? If you want to talk shit, expect a reaction or don't even be afraid of one.
Honestly this is just like bullying, if someone is bullying you, you have to step up and tell them off otherwise they are just going to continue. Sure it's wrong because I may be cursing back but what if the rest of my team is on my side and know a troll when they see one? If this guy is intentionally feeding, telling all 4 of us to die, what's wrong with us responding back? He already ruined the game for all 4 of us which is why I believe we should investigate further to find the root by showing the entire chat log.
Lastly, it may be difficult but I'm sure we'll see more results if there was a level bar for our accounts on how close we are to a punishment. This system can gradually increase or decrease as we have good/bad games. Not that it's to encourage toxicity, but if we know where we stand we will try to be a better role model or even encourage everyone to be more positive. Like have a scale 1-5, we can gain like 50-100 ip if we can stay in the 4/5 zone for 2 weeks. If you're at 1 that means you're getting closer to a ban. To get closer to a 5, you have to receive a lot of honors, and to get closer to a 1 you're going to be reported like almost every game.
Just my 2 cents, hope it helps someone.