Dealing with harassment at the highest level of play is a tricky issue for any publisher. On one hand, and this is my personal view, no one is above the law. If someone is ruining a game by refusing to play and cursing out their teammates, it doesn't matter if they're in placement games or streaming a Masters level competitive match, they should have some form of reckoning. It's not just poor form, but it's bad for the future of the game, as many new players quit MOBAs because of the volatile environment surrounding them.
Often times, pro players are above the law. With tens of thousands of stream viewers, their celebrity status can preclude them from punishment -- something that's been a huge problem in Blizzard's MOBA, Heroes of the Storm. Thankfully, Blizzard is starting to take action.
Community Manager Rathmyr took to Reddit to explain that European pro Mopsio will be banned for seven days, a sanction that also requires his team to find an alternate for an HGC series this weekend. Mopsio was documented on a stream refusing to play while antagonizing his team by Mewn, a popular pro player.
In the case of blowing off steam, I get it. I think people are quick to throw out the "toxic" phrase for light trash talking or ribbing that can be brushed off or muted. But most people would agree that throwing a game or refusing to play is a clear line in the sand. At that point you can't mute someone, you just take an agonizing loss, and either move on or take a break from the game.