At this point I feel like flaming isn't even the community's fault.

Literally not.

What's ruining the game are players who give up the moment they die, troll when things don't go their way, and players who end up with horrendous scores at the end of the game and still not get banned for it. Players who are clearly in the wrong elo and don't demote fast enough.

I am not a very high ranking player myself, but a lot of toxicity comes from placing new players in gold level mmr, and not demoting them fast enough despite them struggling to keep up with the games, coupled with horrendous matchmaking. This leads to a ton of frustration and makes it very difficult for people to keep their cool.

It isn't people's fault they get angry when the ADC runs into a no vision area and gets caught for the fifth time despite heavy pings, or when the jungler clearly has no idea on how to path or gank despite the opponent jungler being everywhere on the map. When the top laner keeps overextending and blaming the jungler, or the mid laner sitting in their lane not knowing how to punish the obviously better opponent's roams, then you clearly realize that your teammates don't and shouldn't even belong in the same elo as the opponents.

It's only natural to lose your calm over another player ruining your day. It's appalling that people still wish others never expressed their discontent over said person's incompetent actions.

Of course everybody has the option to never abuse and play the saints we aren't. But do you know what's even more relaxing than that? Letting go of your frustration instead of bottling it up and suffocating from within. 90% of the frustration comes from the way matchmaking is handled and the blatant balance issues in this game. Fix those and I am sure we'll see far less flaming and verbal abuse.