Now that feast is a going to become a safe space people will just find other ways to harass people on their team that they think are bad or causing them to lose. I know people that might even go so far as to make an alt on other player's servers purely to tell them how terrible they are. Often when queuing for feast during the day I know the result of the match as soon as I see the players on both teams so a 'lost the coinflip', 'time to stop queueing' or other such comment may be made by me or another teammates and it is usually due to one healer being significantly weaker than the other. Granted, the reverse is also true when people say 'free win' etc. The other times I see rage are usually related to mismanaged spoils where somebody picks up way too many and throws a game. In cases like that the person in question is usually called some nasty names. I've honestly never seen anything worse than that so these claims of horrible toxicity seem quite exaggerated.

My question is: If the chat triggers people so much why don't they just turn it off themselves while pvping? Why does square have to mute the chat for everyone?

My proposed solution: A right click>mute for people in the party list, that way people can just mute players that they don't like or consider toxic. While the rest of the team can still benefit from using the chat.