>> He is free to express his opinions of gay people.
Context matters though. If you make these opinions at the workplace and someone feels threatened, discriminated against or harassed, there are legal repercussions.
And I assume this goes both ways. If you have an unpopular view that is expressed outside the workplace but are harassed by your coworkers, there is a risk of legal repercussions on those coworkers too.
Context matters some. But it's not like people's opinions reverse when they walk into the office.
If he is biased against gays, a concern raised by helping fund the removal of one of their civil rights, people can be reasonably afraid that this will eventually affect them in the workplace.
It need not be something obvious, either. Most decisions made by CEOs, especially decisions on who to reward and promote, are almost entirely judgment calls. Do you want to work for a guy who might not treat you fairly? "Yes" and "no" are both reasonable answers.