I don't think it's useful to try to find some blanket rule that works for this case and all other cases somewhat similar to it.
There's a lot of variables in play. The likeliness of affecting change. Eich's worth as CEO. What Mozilla stands for. How his political beliefs and political actions relate to people. The list goes on. Each individual with an opinion on the matter made a call, factoring in the variables that are important to them, and acted accordingly.
If you find Eich's specific beliefs regarding gay marriage to be disgusting enough to suggest he not take the specific position of CEO of Mozilla, go for it. Does that mean that you should protest against every CEO of every company you have stake in, if you disagree with them on some political level? No, of course not. You should make the call on a case by case basis.