I think some people are missing the point, here. This isn't about religion, or free speech, or morality, or oppressing people. This is about plain old CAPITALISM. You know, that agency which has been both glorified and vilified over the decades in discussions about America.
Businesses are in the business of making money. If something is not making you money, then it is not good for business. When one of the most prominent figures in your company takes up an unpopular political stance, he will get public backlash. That's just the way things are. People will boycott. People will protest. It's not good for BUSINESS.
In an ideal world, you could say whatever you want without the fear of it affecting your job in any way. In an ideal world, the workplace and private life would never clash. We don't live in an ideal world. If you donate money to an unpopular political cause, you should expect it to have consequences to your life. Freedom of speech doesn't mean that you have freedom FROM speech. He said that he wanted to support Proposition 8 by donating money to the cause. Other people said, "I don't know if I want to support a company that makes this guy money."
Freedom of speech doesn't mean that you can do stupid stuff without consequences. If I wanted to donate money to a group that believes that black people are inferior and should still be slaves, then people would be right in not wanting to support a business that makes me money. Freedom of speech means that you are free to be stupid, ignorant, arrogant, self-righteous, et cetera. But, it doesn't mean that you are free from the CONSEQUENCES of being stupid, ignorant, arrogant, or self-righteous. We live in a world where you can lose you job from doing or supporting unpopular things. That probably won't change any time soon.