I used to think 10 years ago that as long as people could continue to hide behind the anonymity of usernames and avatars this kind of behavior would continue. However today with Twitter and Facebook it's evolved to the point where people are not afraid to attack people with even their real names in the open. I'm not really sure how blizzard or twitch or any other company can combat this type of behavior beyond IP bans which there are even ways around. I guess if there was a joint force of gaming companies, blizzard, twitch, Sony, Microsoft etc to come together to form a group where if you're banned in one you're banned from all. Would it work? No, not likely but it would at least maybe cut down on this type of behavior. Call it something terrible like Gaming for a Better Tomorrow and have it
Unlike Europe which can barely tolerate people from neighboring countries. Yea if only we were civilized like that. Kappa.
So this is the simplest option and I'm not sure why it hasn't already been done, but just make it standard to not have the chat option availble on live srteaming!