To me this is not a ban able offense since players are given the option to mute each player both on their team and on the enemy team, or further more they can get rid of the entire chat feature itself in the settings box.
The mute feature is a band-aid solution, and it's meant to prevent a player from suffering further ill-effects of chat misbehavior. It is not there to give players an exemption from the rules that they agreed to at account creation.
Whether you like it or not, everyone who makes an account on League of Legends signs up with the promise that they will not abuse the chat feature to misbehave and flame other players. Whether you like it or not, it is a punishable - and, if necessary - bannable offense. Don't like the rules? Them's the 8r8ks.
I believe that every player who was permanently banned from the game for purposes only due to "toxic" in game chat behavior such as cursing and or trash talking teammates or opponents should have a second chance in this game since technically they have not actually broken any rules in terms of making the game enjoyable.
I'm not sure where you're getting "technically" from, because they did in fact break the rules, and they did make the game unenjoyable for other players. If they didn't make the game unenjoyable, they wouldn't have been reported, and if they didn't break the rules, they wouldn't have been punished.
I seriously recommend you read the Terms of Use - Code of Conduct as well as the Summoner's Code, as both constitute the rules and behavioral guidelines you're expected to follow in League of Legends.
Since riot has the mute teammate feature players can simply mute their teammates who prefer to take out their aggression over the terms of typing in chat even though the chat box is suppose to be used for team work and planning, however we players know that this rarely occurs in lower elo and especially in higher elo.
Players should not have to mute other players. If you prefer to take out your aggression in-chat towards your teammates, then guess what; players can mute you, and they can also report you. You're not allowed to flame, period. The mute feature does not exempt you from that rule.
Additionally; I'd really love to see some statistics about the usage of chat for coordination/teamwork. I doubt it's as low as some people like to sell it as.
Personally Riot should spend less time focusing on banning players for things such as toxic chat behavior for this doesn't cause any real harm unless these players are telling other players to kill themselves repetitively for this is a different style of aggression.
Why do people assume that Riot is strictly focusing on chat misbehavior? It's not like they have extremely limited resources and choose to funnel all of them towards chat misbehavior. The IFS - the system that handles chat misbehavior - is automated. So with the exception of cases pulled from the IFS for audit/manual review, they really aren't focusing on chat misbehavior any more than they're focusing on anything else.
Riot in fact should spend majority of their time banning the players who truly cause major issues in this game being those who win trade, and purposely throw games to help streamers out as well as boosters.
Again; you're assuming that they aren't trying. Unfortunately, non-chat offenses aren't something they can just set the IFS to track and punish reliably. Chat offenses are easy; win-trading, trolling, intentional feeding, etc.? Those aren't half as easy. And as it were, simply saying "focus on this instead of chat" isn't going to make it any easier.
The video above is proof that this issue is apparent yet people prefer to say that those who are toxic in chat are the ones who ruin games.
Both are players who ruin games. It's not an either/or situation, and I don't think I've seen anyone even remotely suggest that wintraders/trolls/etc. don't ruin games while flamers do. Both ruin games, both are awful, and both deserve punishment.
Riot please unban those who made mistakes in chat and focus on those who truly cause issues in this game.
Again; they already are focusing on gameplay misbehavior.
And as for unbanning flamers; if they got permabanned, then they didn't just "make mistakes in chat". They made a ton of mistakes. Constantly. Enough so that Riot had to permanently remove them from the game.
At that point, that's not "making mistakes", that's deliberately flouting the rules. And those players who openly disrespected the rules, even after countless warnings, they're not getting unbanned. Period. If you can't be bothered to play by the rules, Riot can't be bothered to have you playing at all.