Has he ever said anything against gays? Being opposed to gay marriage is not the same as being opposed to gays.

Yes it is. Lets not make useless differences here, it is. To think there isn't is somehow thinking someone having fewer rights than you do is still legally equal to you.

Does being against polygamist marriages make you against polygamists?

It depends on what you consider the goal of marriage, or what the rights specifically are. Seems to me there are lots of people who can't marry, for example children. Why do they have "fewer rights"?

What about people who think marriage is silly anyway?

People change too. You can't hold it against someone all their life because they donated $1000 to prop 8. For the rest of his life, people will look at Eich differently simply due to the small donation amount many decades ago.

And he can speak about it if he does? It's okay to change your mind. He's had all week to talk about it, if he has already. But he hasn't.

If you're worried about his future career, I understand. But if he changes his mind he can equally talk about it with potential employers/partners. If he doesn't, then he gets to live with the consequences of his choices the same way someone who is out about their sexuality does.