Here's another good hypothetical. A whole bunch of Muslims move into the US, and begin to outnumber the Christians here. They pass a law that Christians can't marry other Christians. They even vote in amendments to state constitutions enforcing this. "You have the same rights as everyone else", they say, "to marry a non-Christian. We define marriage as a fundamentally Muslim thing. You can't ask us to redefine marriage to suit your tastes. This is a democracy, where people vote on how they want the country to be."
Suddenly, you are in the exact same situation gays are in right now. Doesn't feel too good, does it?