I wouldn't want a member of the KKK running my organization either, and I would imagine most minorities would speak out about that as well. Racist or anti-gay, a bigot is a bigot. This isn't about politics or personal views. It's about denying human beings their deserved civil liberties for no good reason at all. Would you want to work for someone who hates you enough to force a law to break apart your family?
Listen, I get where you're coming from. This is an important issue for me too. (As an aside: I have spent an inordinate amount of time working with one of the world's largest human rights organizations, including time on the board of directors for one of its structures.) I like and appreciate your passion to fight the good fight.
But! Be careful when you reach into your toolbag to fight that fight. The ends never justify the means. If we violate one person's rights by trying to protect another person's rights, we'll descend into chaos.
Always be respectful that in 7+ billion people, we're going to have a lot of opinions.
We must stop behaviors that are directly harmful. But we must always also protect people's opinions.
They're important. You have the freedom to believe whatever you want to believe. The minute that opinion crosses into a behavior -- boom! You can drop the ax. People have the right to any opinion but not any behavior. Do you see? If Brendan wants to donate money to a bill that would do x, he can. If he punishes an employee because they're x, that's wrong. (And you cannot jump in and say, "He will have a behavior because of his opinion.")
The way to handle this is to respect his opinion and be on guard that no behavior follows from it. Period. Put that important passion instead into educating and enlightening the populace. Put it into doing positive work.
Forcing Brendan to step down because he donated money to a legitimate political proposition is witch-hunting and shameful. This issue deserves better than that.