I put marriage in quotes because we're really not talking about marriage. We're talking about civil rights.
If I told you "No insurance benefits because you're not Catholic" you'd be (justifiably) outraged.
If I told you "No, you can't adopt a child because you're Jewish" you'd be (justifiably) outraged.
If I told you "No, you're not the next of kin because you don't believe in the divinity of Christ" you'd be (justifiably) outraged.
As long as "marriage" is the measuring stick government uses to determine what people can and cannot do, we can not discriminate about who is allowed to marry. Once it's not just a matter of religion, but a matter of public policy, there's no place for a religious standard.
Marriage is a sacrament in the Catholic church but that doesn't mean only Catholics get to be married. That's an idea so ludicrous, you laugh out loud.
That is in effect what we are saying though when we say "marriage is a only for heterosexual couples." We are investing a civil right with a religious requirement.
As a practicing Catholic, I value my freedom of religion very much, thank you. I'm not in favor of returning to state sanctioned or mandated religious practice of any kind.
Your opinion may vary. Express at will. Personal or vile comments will not see the light of day.