The very nature of this game breeds toxicity...
Don't get me wrong. I'm not asking for changes but here is a little insight into how this game is inherently toxic.
Imagine that you were playing an FPS but every time someone died the other team got more powerful. Their bullets hit harder, etc. That is essentially what's happening in this game. So of course people get mad at the person who is feeding because it's making the opponents stronger and thus taking control away from the feeders teammates as they are unable to play effectively against the fed opponent. No one likes to feel they can't impact the game and this leads them to blame the feeding teammate and get angry with them.
I don't know what would fix this, and like I said I don't care if it gets fixed. Actually I don't even want it fixed. I'm just saying that this core mechanic of snowballing in league IS the reason that this community is the most toxic ever.
God bless your nerd raging hearts.