Don't DO =/= Don't SAY
You probably agree that the worst detriments to the community are those players who do one or all of the following:
- Rage Quit (leave because they are doing poorly or don't like the match-up)
- Intentionally Feed (hand kills to the enemy because they're doing poorly or don't like the match-up but don't want to get automatically leaver-busted)
- Cheat (use scripts or other third party software in order to give themselves an unfair advantage)
These are the worst offenses because, try as you might, there is nothing you can do to fix the situation when someone does these things. And because there is nothing players can do when another player does any of those three things, it is-- and should be-- left up to Riot to ban said players from playing the game.
However, there's another reason players get banned for which no punishment should be enacted by Riot: casual gaming speech. What inexperienced gamers may refer to as "toxicity." Whether a player is being toxic is completely subjective, and made even more so by the lack of a voice chat in this game. Knowing this, Riot implemented one simple function that completely removes the subjectively perceived toxicity without any effect on gameplay whatsoever-- the mute button. It takes a grand total of 1.5 seconds to hold TAB and press the little speaker icon next to someone's name, or the little "!" icon if you feel they're incorrectly using pings.
Yet still, Riot will ban players for using their chat function in a way that another person disagrees with, even if said player was the biggest contributor to the team's victory. This isn't right or fair to either party. The one who speaks should not be punished simply because someone else disagrees with them, and the one who disagrees should not be rewarded for refusing to use the mute function.
For now though, Riot takes the stance that the feelings of those most prone to having their feelings hurt are justice. Maybe eventually they'll realize that a competitive, team-based game such as this will always create negative feelings when allies mess up and switch their stance. Or just outright remove the chat function, like they did for the public chatrooms years ago.
It must feel really nice, knowing you can basically steal and burn upwards of hundreds of dollars worth of content from another player just because they said something you don't like. Think about how you'd feel if someone hacked into your account and changed the password next time you're a little upset that someone pointed out the fact you're building Sunfire Cape against Rumble.