No one has a right to hold any particular job, especially not one as public facing as CEO. You may have the right to work, but you don't have the right to work in one specific job at one specific company.
Of course you do. You can't legally be fired for saying, "I am a member of the Republican Party." Your political views (and that's what, in the end, this is) are protected, not when they are shared by everyone, but specifically when they are not.
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.