I think the notion of not photographing their wedding is a phony principle stand. Jesus spent most of his time with sinners - not to condone their sin - but to be a light.
I also think they are falling prey to a scam, and by not agreeing to do it, they are stepping right into the doo doo layed out in front of them.
I would go to the mat for any owner to do as he/she pleases with a business, a property, etc. And I absolutely confirm their right to do whatever they want to to and refuse service to whomever they want to refuse it.
Are you denying MY RIGHT to say it was a foolish business decision?
Are you saying that Jesus would attend an event where two men pretended to get married?
Jesus also told believers not to cast their pearls before swine. And, when Jesus did deal with the unrepentant, He rebuked them.
And, nowhere in the Bible does it say Jesus or believers should take an action that validates sin, which taking photos at homosexual "wedding" would do.
So, based on that logic, perhaps ministers should be performing gay weddings as a means of showing homosexuals the light! Makes as much sense as assisting two lesbians by taking pictures at a wedding ceremony.