No, churches should not be forced to perform gay marriages if they are against them.
Why?
There are plenty of other churches who will be more than happy to marry them (and get the fee for the wedding).
Should bakers be forced to bake cakes for gay weddings if they are against them? Why should churches get a pass? If you think that's how the First Amendment should be applied, do you see the problems that introduces? Should churches that believe in human sacrifice get to skip the laws against murder?
Hyperbole much?
Not at at all. It's a legitimate question about the principles we're dealing with. It's a hypothetical to test the soundness of the premise. If a there was a church, of let's say - four people - who were into human sacrifice. Would they be able to ignore laws against murder? Of course we would not (or at least I'd hope you'd agree with that assumption) allow them to do that.
The bottom line here is that the point of the First Amendment's religion clause is not there to exempt religions from the law. It's there to prevent government from enforcing laws that target religions for special treatment (either for, or against). Our founders had seen the problems with letting religious power and government power join forces. It gets ugly quick. So the included a "wall of separation" to prevent it. But the intent was never to give religions a 'get out of jail free' card.