It was a wedding cake they where making. They make wedding cakes all of the time.
They are not a machine. They are people providing goods and services. And they have the right to express their values in that capacity. This has clearly been upheld in many other cases without it being seen as discrimination. I do not have to support people in doing something I philosophically disagree with and nobody else does either because in general that's what freedom is.
It doesn't matter what you think of a person. If you offer a service you must offer it to everyone. Not only that but it does matter what they do with your service unless it is going to harm someone.
The person who will be harmed is the person making the cake because they will feel like they have not obeyed their own set of standards. That sort of thing sticks with you. If you offer a service, you are free to offer it to anyone you want to or don't want to. It may not make for good business, but you are allowed to do it. And you should be allowed to do it. And it isn't discrimination if you decide you aren't going to do so because it conflicts with an important part of your identity. Especially if it is not a life saving practice and even then maybe. A wedding cake is so incredibly inane and easy to get other places. The only reason to make a stink over a wedding cake is because you have an axe to grind with religious types and have no conception of what freedom of identity practice should be.
If a black person owns a hotel he cannot refuse membership to the KKK unless he have reason to think they might burn his hotel down or kill people in it. If a Christan sculptor is ask to make a Jesus sculptor knowing that those people are going to blow it up he cannot refuse.
Do you have anything to base this on or are you simply stating what you feel it should be? Because if that's all this is, then great. You do that. But unless you find other evidence, it seems unlikely anyone will follow those rules.
t does not matter what people are going to do with the item they brought. It is none of your business. Those guys make cakes for a living. They also make wedding cakes for a living. It is none of their business what is the wedding cake is use for make it and STFU.
And therefore their name and skill is on that cake. It means they are endorsing the activity in some small way. Most wedding cakes are highly intricate and specialized. It is a creative act.