Guess what, Bob? Protection against firing over such matters is one of the things unions work for. If Mr. Damore had worked for, e.g., The New York Times and been threatened with firing, the Newspaper Guild rep might have regarded him as an anti-social, unwoke reptile, but would have fought his case against management, all the way to the NLRB if necessary.
I should say that you considerably overestimate the leftward lean of American unions.