I've discovered the secret to avoiding toxicity.

The reason I feel the community at large is so toxic boils down to this simple fact: Many of us carry our games with us. What I've found is that when I carry a stupid loss into the next game, I'm more apt to assume A. my new team will be as ridiculous as my old one, B. my new opponents will be every bit the assholes my last opponents were, or C. both. When I make that assumption, I tend to try less. "Why bother?" I think. "No one wants to win anyway."

For me, I tend to keep my toxic thoughts to myself. But for those who find it harder to do this... Imagine that most everyone is carrying their games with them. They all assume the worst of eachother and jump to the worst conclusions. When you're already assuming your opponents and/or teammates will be jerks, and then one of them acts on their similar assumption, you're quick to lash back as you were already expecting this sort of behavior. It devolves rapidly, and if everyone is doing this... Well, the whole community becomes toxic.

TL;DR, leave your last game in the postgame lobby.