EEOC makes it illegal to discriminate based on race, color, religion, sex, national origin; why can't political views and speech said outside of the workplace be a part of that?
Free speech protects you from the government, not your peers.
In many societies and for many people, religion is not just a set of "things you believe", but is deeply connected with cultural and/or ethnic identity. The best example in the US might be Jews, which are either a race, culture, ethnicity, religion, or some combination of all of the above. But the same principle can be true for other groups as well.
So, yeah, I'm pretty sure he violated that. And Blizzard's response has too. It's really just a catch-all trivial to violate provision.
As a separate note, the player and hosts would likely be considered to be contractors, not employees.
If you try to sue someone for violating a law that doesn't exist, they will make a motion to dismiss for failure to state a claim, and the judge will throw out the lawsuit.
That's not to say it is right or acceptable, but it isn't illegal.
Source: https://www.nolo.com/legal-encyclopedia/can-employers-discri...