The vast majority of the community are decent people, some are actually NICE. (I know, right?)
But the the way the game is changes the perception of how much of a problem toxic players are. For example if you look at CoD, another team game with an infamously toxic community that's not a MOBA, it's not as big of a deal to get someone toxic on your team for several reasons:
- Toxic players in CoD can be kicked from the match and replaced with another player.
- CoD matches tend to be much shorter than your average game of League; especially SR. You end up spending less time with an individual toxic person as a whole, and if you lose a match because of a toxic player you don't feel as if you wasted that much time.
- Even if toxic players cause you to lose a match, you can still get rewarded based on your personal performance in CoD. (Champion mastery tried to emulate this, but since there's very little to be rewarded with it's not making up for that loss of MMR)
So even though CoD more than likely has a significantly higher amount of toxic players than League, CoD has several ways of minimizing the impact of their toxic behavior. League has one: The report button, only available after they've destroyed your fun and wasted 20+ minutes of your time. The mute button is a grey area; it stops some forms of toxicity, but not all of them like AFKs or feeding.