In the case of trolls and AFKs, you can still have a fun loss. You can even have a hell of a comeback. A game with a rager is like bleeding out through a paper cut. You're almost never going to make a comeback, and the whole thing is hell in the meantime.
I know people get competitive. It may be "just a game" but the point is still to win, I get it. But raging is more detrimental to that than trolling and AFK.
Or, here's another way to look at it. If you're annoyed by someone trolling, leaving, or doing poorly, it's probably because you know what you're doing, and you know what they could be doing if they wanted to win. That's a good thing. It puts you in a position to lead. In fact, you probably are leading, whether you know it or not, whether you mean to or not. So as soon as you get pissed and give up on the game, you're leading your team into the gutter.
The alternative is to take a breath and look again. So you've got a Teemo ADC or some shit. That's bad. But what could your team do to win? Where could you push and advantage, even being a man down? How can you exploit the other team's weaknesses with just 4 members? If you focus on that, I bet you'll be surprised how many throw-away games you end up winning.