So then the two women get married, instead of celebrating profits, and serve the cake you baked. You have baked a cake for a same-sex wedding. And you'll know because the two women will give you good reviews for how good the cake was. More same-sex couples will come to you to bake their wedding cakes, with a wink and a nod. Your same sex customers will sing from the mountaintops as to how good your gay wedding cakes are. More same sex couples will come to get their cake from you. You will be known all over town as that guy who bakes really great cakes for gay weddings.
How does this put you square with your religious objection? Does a priori ignorance grant you some special celestial immunity? Does a wink and a nod set you right with the Lord? How long can you pretend to not catch on to the fact that your wedding cakes really empowers same-sex marriage?
If I am lied to believing that my cake would not be used for a gay wedding ceremony, and it in fact is, then I am not the one who committed the sin. I didn't lie.
I believe in honesty. If they were to tell me that the cake would be used for a gay wedding ceremony, then I would not sell it to them. On the other hand, if they fibbed, and told me that the cake was intended for a business party, and I was convinced, then I would sell the cake to them, regardless if I knew that they were gay. I trust everyone, however if I believed that I was being misled, for instance if they started chatting about a gay wedding amongst themselves, then I would not sell them the cake.