I agree. I think it is a problem not just with Blizzard, but with all online games.
Just look at league or dota, or keep your mic open and unmute everyone in PuBG. Or hop on call of duty and try and socialize. You'll realize how garbage most people are online.
However, I do think more cooperative-centric games are a little less toxic (World of Warcraft for example) than these other ones. I think the most toxic players tend to gravitate toward the competitive "team deathmatch" type games.