You assume that the baker is 'offering to bake cakes for all different kinds of weddings'. What if the name of his store is "Straight Cakes Only"?
I'm not assuming that, this is what I said.
It's the same thing for a baker that offers to cook wedding cakes for all different types of weddings.
It applies to the baker who offers their baked goods to the public. Though, if their name was straight cakes only, they would be in direct violation of an anti-discrimination law depending where they were located.
I just happen to think something like a baker is more of a contractor. I think you should be able to walk into his bakery and buy anything that's already made no matter who you are, but if you go in and ask him to make you a cake that has something offensive on it (offensive to the baker, that is), he should be able to refuse taking that contract.
If the baker doesn't want to bake something because it's offensive, then that's a non-discriminatory reason! Though I'm not sure the argument is there to make that baking for a gay couple is "offensive" even if you disagree with the lifestyle. Maybe that could slide in some way but I'm doubtful of that.
If a baker is making wedding cakes for only straight couples (provided it's some religious bakery that only bakes them for these specific types of couples that doesn't include gay couples because that would be open discrimination on a public service as well), then they wouldn't be necessarily offering a public accommodation. It depends how their doors are opened for business. If a gay man could walk into a bakery and buy a cake or ask for a cake to be made (for a birthday for their partner for instance or something) and the baker does it, how can he then turn around and say oh I don't want to make this three layered cake for a wedding that will only have two male figurines at the top but the rest of the cake is no different than any other wedding cake I've made. To me, that's hypocrisy.
But this discussion about being a private contractor is really just factually inaccurate IMO of course. If the baker is in the public services industry and is offering to bake cakes for a variety of people and advertises him or herself as such, then why should they be able to say, ohhhh no, not gay people. I can't have two male or female figurines on top of MY layered cake. They are as much contractors as a business that offers catering to the public. Again, they are both in the public services industry, they aren't allowed to discriminate contrary to the law.
How would you feel if a bakery refused to make a cake for two black people getting married because they hated black people and were openly racist? It's the same principle, just probably not as extreme of an example when you consider how racism and discrimination based on sexual orientation are viewed.