Bottom line, how do people vote against human rights? It's just incomprehensible to me.
Because they do not see it as a right.
Getting allowed to marry the one you love isn't a right? Of course the real answer is that those people feel homosexuals made a "choice" and shouldn't be allowed to dirty the "institution of marriage" on their whims and fancies.
Well, according to loving v. Virgina it is a right. It's wouldn't take much of a change:
I have yet to see anyone provide an even vaguely compelling argument as to how such unions would harm the marriages of others, or otherwise harm society in any way beyond the hysteria of bigots (and the existence of groups like the KKK was not a reason to eliminate civil rights). People are still free to be bigots. Churches are still free to turn away couples for any reason, no matter how irrational, including skin color. Justices of the piece should be willing to uphold the law, and bias against same sex couples should be viewed as repugnant as those against interracial couples.