I can't support this one. Open for business to the public, serve the public.
I think the greater good would be to inform the individual of your religious objection, but if you are required to provide the service you will not keep the profit as that would be profiting from (as the florist see's it) sin. Inform the customer that all profits will go to an anti same sex marriage organization or candidate.
Put the ball in their court.
If the gay couple wants to proceed, collect the hefty deposit and get on with business.
Win/win
Here's the thing..when you are catering an event, that is essentially advertisement. That's why people seek high-profile customers. Because a lot of people attend the event and see your work, and it generates business. You are also ENDORSING the event, because everybody knows that you created whatever it is (and usually, caterers also serve and always set up).
People who are CHRISTIAN cannot abide by their faith and participate in sacrilegious events. There's nothing DISCRIMINATORY about just saying "No, we don't want to do that". This is not food that's being prepared to eat on the premises. They are not kicking assholes out of their stores. They are known to have served and hired homosexuals. It is just a matter of them having a RELIGIOUS OBJECTION to actually participating in an event that they believe is sacrilegious. There are other bakers and pizzerias available for the homo crowd. They are not being *excluded* from purchasing or hanging out in the establishments.
We have the RIGHT to refuse to endorse those things that we have religious objections to. We don't have the right to attack, throw rocks, spray paint, or vandalize the premises where those things are held. But we can say "We will not go to these events or participate in them" and that is NOT illegal discrimination.