Saying "Happy birthday from your wife" doesn't go against anybody's beliefs. It goes against their bigotry.

There's a difference between refusing to write something you believe is untrue (like Jesus is the son of God) and refusing to write something that is undeniably true but that you are bigoted about.

It's funny, and sad, how religious freedom is only ever invoked in service of bigotry. Despite all of Jesus' teachings to be loving and accepting, despite him never preaching a word against homosexuality, despite it not appearing anywhere in the Ten Commandments, Christians only ever talk about their "religious freedoms" when they want to discriminate against gay people. And before that, black people. And before that, people who were the "wrong kind" of Christian.