There exists in the United States an entire economy that exists between and among private individuals. They buy and sell and associate only among those people with whom they feel comfortable. Anyone can gather together with the likeminded and conduct business. They need only keep the transactions private and legal.
I find the bakery cases fascinating. A couple's wedding is a public display of a commitment to intimacy. An invitation to participate in a wedding is more than just a business transaction, it is an invitation to participate in a sacrament.
How does one legislate such a thing?
I don't see how you can say that a cake maker is being invited to participate in a sacrament any more than the printer of the invitations is, or the taxis that bring guests, or the company that made the mother-of-the-bride's gown.
Those people sell stuff. You don't "participate in a sacrament" for money. Moreover, for many of us, marriage is not a sacrament.
One legislates business. Why? because businesses WANT the protections that government provides to businesshood. The laws that support the rights to incorporation, liability protection, business tax treatment such as the writing off of expenses.
So Businesses WANT public accommodation on themselves and their activities. In return, they are required to provide it to the public which grants them their accommodations. You want public business protections? You must serve the public, period. You must serve whatever you serve to anyone who asks. But of course you are not required to serve things that are not on your menu. Only that whatever you serve, you serve to all.
There is no sacrament here. If it were about something other than money, they would not take money, set prices, ask for tax deductions on those incomes. They would depend upon donations and claim each one as a gift at full tax rate.
But that's not what they do. They WANT the public to accommodate and endorse their business. And we do, in return for certain standards. If they don't like that public standard, they can be a private club - and get no tax deductions.