Banging on about a controversial subject that can cause upset and disruption in a work environment. Does that sound very professional, or something that a smart person would do? And do you really want that kind of person in your team?
He didn't insult anyone, although some amount of his coworkers did feel insulted.
The difference between these two things is significant.
Put differently: We are going down a dark road when someone simply being offended by pretty mainstream views mean those views are the problem.