You see same-sex marriage as a human right. (You would surely agree that same-sex marriage was a right even were it not a legal one.) To those of us who believe in human rights, which undoubtedly includes Eich, that would make anyone who took action to deny anyone that right unethical.

The problem is Eich doesn't see it as a human right. Indeed, to him, it may be the case he sees same-sex marriage as unethical. (We don't know what his objections are.) At any rate, he has no reason to find the support of gay marriage ethical or the opposition of it unethical.

There is no objective morality that tells us who is right or wrong here. There's no divine tablets we can all interpret listing out all our rights.

You can't stop at "same-sex marriage is a human right" and "opposing gay marriage is (ergo) unethical." That just leaves you talking right past people like Eich. It doesn't advance the argument or the cause - it just labels people as stupid or bad.