The notion that Riot should support him simply because he makes videos is far-fetched, as they don't have much benefit.

You're understating this in a pretty big way. Dunkey is probably one of, if not the most viewed youtuber who put out a lot of League content. That is guaranteed to bring a huge amount of traffic. I'm not going to weigh in on whether or not they should support him, but it's stupid and ironic that that Malphite went on to play games while Dunkey was banned.

toxicity really does come from the person themselves

Do you actually believe that toxicity only and absolutely comes from the person? That's got to be one of the most naive things I've seen posted on this subreddit. One of my friends, who is probably the most mild-mannered and nicest guy I know, has actually been rolled back by Riot for raging in one game. Before playing League for an extended period, he would almost never curse, and if he did, he would substitute it with something like "fudge" and the like. He doesn't really do that anymore, we used to think it was really silly and I think he's over it, but when I heard he was rolled back for raging no less, it was a pretty big shock. It's funny because I have never been so much as temporarily banned, and one of my other friends who is probably a clear-cut example of a "toxic" player hasn't been rolled back ever, I'm not even sure if he's been banned too often.

That's all anecdotal evidence of course, but witnessing it secondhand, I would have to agree with a lot of what Dunkey says. The game (or at least ranked solo queue) and the Summoner's Code is built in such a way that incentivizes toxicity, and passive aggressive behavior. Games last a REALLY long time, and there are only five positions in a five on five team game, so people's patience eventually wear thin. You go rank, queue low, so ok, you'll have to probably play a role you don't want. That's fine for the short term, but how many games will this happen? How many of those games will you win or lose? How about the games you actually do get your desired role, how many will you win or lose? Was it your fault? Was it your team's? How many of those games were you actually all outplayed? How many times when you queue high will someone say they will feed/afk if they don't get your position? Sure, just report them in the end, but you are forced to spend on average 45 min or an hour long with a huge disadvantage (mostly because it's one rallyer saying you can still win and the other passive players following along). 4v5s are not unwinnable, but they are hard against people who have half a clue on what they're doing. And that's just with an afker, a feeder means you have to pray the other team commits suicide and lets you run over them.

Maybe you're handling all those questions splendidly on your own, but that doesn't mean your, at least three (a majority) teammates are. That doesn't mean the other team isn't handling it well. How good does it actually feel to win against another team that has a blatant aggressor? "Sorry for your loss, I'll report him after the game" is all you can really feasibly offer before you take an undeserved win on them. So many games I have played, I play mild-mannered, I don't respond to shit talking, try to play not on tilt, try to calm down infighting with a passive stance (I don't talk anymore if it's clear they won't stop), or I try to carry my team so they can ignore it all-- but it wears you down. A lot of the times it's one jackass picking on an average or underperforming player, and when you see the victim take matters into his own hands and decide that everyone else has to suffer because he ultimately cannot handle the blatant bullying, that is what really sucks to watch the most. I feel like this written out is what is behind a lot of the reasoning behind the decision to quit League, not just from Dunkey's perspective. The chances of your upstanding behavior paying off is horribly slim, until it's time you really can't contain your emotions and you become "toxic" yourself. Maybe there isn't a single bad or petty bone in your body, but just think about all the streams you probably have watched of the player ranting about how retarded someone is being? They have a slight advantage though, because they have an audience other than their teammates to rant to.

I'm going to try to stop here since it's starting to get really long. I can go into a lot of things like how this game has literally ruined some friendships, or how many babies it has eaten, but I won't. I'd like to end it with that I've played League for over 1600 hours of my life, since Xin Zhao and Akali were released as new champions. I've quit maybe 2 or so years ago, around Season 2 maybe, and outside of going back to take plat on Season 3, I have only played on and off since, and mostly only with friends. The reason being pretty much almost if not all the factors present in Dunkey's video. I can't see how so many people here actually think that League isn't a factor to player toxicity. Originally DotA was a team game you usually played with friends as a team, and you only really played by yourself to practice or get a feel of the game, and even then it was among other players who probably never spent as much time with a wide access to information on DotA as they would go on to, or as people who start on League have. It was a little hard to get an actual game going, but you didn't have to COMMIT to the bullshit that League heavily and even threatens you to commit to, and you and/or your teammates were NEVER convinced by the Summoner's Code or shitty posts on reddit (or at least there used to be) that said "Never give up guys, I just got out of a 4v5 game with inhibs and base towers down but STILL won! I won't bother to mention how the other team literally threw the game though!". Aside from watching pro games, the irony is that ranked solo queue is now and probably forever the main platform for semi-competitive League of Legends, not team ranked queue, and this will always be a huge reminder of all the reasons I quit this game.