Really?
Yes, there have been many examples. The one at Cisco stands out in my mind. There was a guy who was fired for being against gay marriage. His boss found on the internet he had written a book stating that. (was not high profile) The boss said that he was an excellent employee, great at his job, and he had never mentioned same-sex marriage, or anything controversial on the job. He personally liked the guy. But the fired him because he was personally against gay marriage.