Exactly the same basis as refusing a gay couple: even if his religious texts say they are an abomination, none. He may express his opinion to them, freely and frankly, but under your laws, he can not refuse service to them, as that breaks the law, as it was determined to do so back in the 1870's. There is almost 140-150 years in which this has now been acknowledged as the way it works now: the first does not protect you when you break the law.
And again, its not removing the rights of the baker, its saying the business of the bakery must serve all customers equally. Had the bakery two bakers, and the first refused but the second didnt, there would need be no court case, as the bakery would not have broken the law. The problem for him is that he is the owner, so he got sued not as the baker, but as the bakery. No legal problem for an
employee, only the
employer.
Commerce is not negating the constitution or the amendments to it. the law simply says that in this case, a business is not a person, so must adhere to the laws of business, not the laws of a person. The individual has, and continues to have the rights given by the constitution, so long as you dont break other laws, while a business has its own set of rights and responsibilities which arent written in the constitution, but still needing to be followed.
Employer v employee, business v individual. different circumstances, different rules.
PeterZ wrote:What basis does the baker have to refuse making a cake depicting an interracial couple? On what basis does he assert his 1st Amendment protection?
If he has religious issues, then prove it with doctrine or text that support making such a cake violates his conscience. If unable to prove it, he has no protection. The baker simply disagrees with the practice.
The protection of the 1st Amendment requires two things: that the expression in question functions to convey an idea/symbol and that refusing to perform that expression violates one's conscience. Should the baker have engaged in other activities that are contrary to the religion he purports to adhere to, then his claim is likely false and he cannot deny the couple even this service.
A pacifist has the same protections if asked to express himself/herself to convey violence. Even if the requester is part of a protected class.
To assert that by engaging in business, one has by default given rights granted by the Constitution is simply ridiculous. That means that anyone accepting a wage has given up their Constitutional rights. What is a wage except engaging in commerce? As an employer the Government can legally punish/fine an employee beyond termination or what a private employer could assess that it could not do to someone not employed with it.
Asserting commerce negates Constitutional protection means only the independently wealthy truly are protected. That cannot be what the founders intended.