Orson Scott Card is a Mormon.
He doesn't like gay marriage.
Those two items are consistent with each other and one sort of falls from the other.
He's writing for a Superman comic and because he's anti-gay-marriage he MUST BE FIRED!
It's especially ironic in he's called the press for gay marriage as the "death of democracy" and gay rights advocates (militant types, one each) are demanding he be fired, summarily. Don't like the author, don't buy the book and if there's enough of that the situation clears itself.
OK, ACLU, where are you defending Mr Card's right to freedom of religion? He didn't turn the job into a soapbox for his views, he expressed them personally not professionally.
Oh right, I forgot, you don't do religious freedom for those WITH religion...
PS: I've actually read what Mr Card has to say about gay marriage and it's not as bad as has been made out. He's got an opinion about the source of homosexuality and describes it in a manner that's clinically abrasive. The science about it is not decisive, so he may yet be proven right about it. The rest of his rant is about the systematic destruction of family by government and how gay marriage advocates seem to be on the vanguard of that movement. The things he cites as being corrosive to families are certainly being pushed by the persons he identifies.
That's his opinion and he's welcome to it.
Marriage is broken in America already and whether we let gay people marry is not going to make it worse, or better.