Another half-step back
What are the criteria?
I think in the Deep South *if* the "gay bakery" found it difficult to buy supplies there are more than ample legal remedies for that.
Those are precisely the remedies you want to eliminate.
In the example cases the couples didn't ask for explicitly offensive cakes. They asked for the same cakes/flowers as other people get. As AScott already pointed out, civil rights law does not address the nature of the product or service being denied, only the status of those to whom it's being denied.