Well, just another highly controversial thing dealing with the Gay & Lesbian community. IMO, the couple had the right to not do the wedding due to their Christian beliefs. But, it does seem odd that they would allow the Reception. We don't believe in Gay Marriage and that is our choice to feel that way. As for me, I use to work for a Lesbian couple, in-charge of their horse boarding stables. But, when boarders started giving them some slack for walking around holding hands and arms around each other, it was time for this dude to move on. I didn't like seeing this "out-in-the-open" affection either, but didn't say anything.
I remember walking into a sporting goods store wearing the baseball cap of a competitor store and was asked to take the competitor's cap off. I didn't give a "hassle", just took it off and smiles and continued shopping with my wife. The way I looked at it, it was their business and if they didn't want to see a competitors baseball cap in the store, they had every right to ask me, and they did ask me nicely, to remove it.
I believe it's up to the business owner/owners how they want to handle their business and who they want to serve. Like I said, IMO.