I've been a proponent of keeping /all chat on for many years

I clung tenaciously to the belief that there might be some positive interaction in /all chat, defending that choice through thick and thin. What if the enemy is legit impressed by a cool play from our team and wants to give us a tip of their hat? What if they want to be generally friendly and ask us whether they should have pizza or a burger for breakfast? There are so many nice things someone could say to a stranger on the Internet, even if that stranger is an opponent in a game.

A few days ago, though, I realized that the only thing I ever see in /all chat is complaints from the losing team about why they're losing (team sucks, opponent's champ is broken OP, etc.), or trash talk from the winning team about how awesome they are and how terrible trash noob garbage the enemy team is.

I discount, of course, messages from me, because those are positive. I don't trash talk the enemy team or my team; the only thing I say to the enemy is some sort of condolences when they lose ("that was honestly a tough matchup; I dunno what I would've done in your place").

All I ever see other people type in /all chat, though, is negative. Literally everything. Every time. No "sweet hook," no "my friend says pineapple does(n't) belong on pizza," no "henlo, i am birb." So I disabled it, and I have not been trash talked by the enemy team nor have I seen my team trash talk the enemy team nor have I seen anyone complaining to their enemies about their allies. It's rather nice! It doesn't stop things like emote spam, of course, and there are still the usual issues of people trash talking their own team in allied chat, but still, it's an improvement. If you haven't yet disabled /all chat, give that a try.