What does the power to regulate interstate commerce have to do with illegally meddling in a transaction that does not cross state lines?
Heart of Atlanta Motel, Inc. v. United States
Having observed that 75% of the Heart of Atlanta Motel's clientele came from out-of-state, and that it was strategically located near Interstates 75 and 85 as well as two major Georgia highways, the Court found that the business clearly affected interstate commerce.
I think you'd have to admit that that was quite a stretch, to support an argument that the federal government had any authority here by way of the commerce clause. It's certainly well beyond what the authors of the Constitution were thinking when they wrote that clause in the first place.
Does any similar principle apply here? Was Sweet Cakes Bakery located in a different state than that in which the pervert couple lives, that were seeking a homosexual mockery of a wedding cake? Is there any evidence that Sweet Cakes Bakery received most of its business from out-of-state customers?
If the Commerce Clause was intended to act as such a catch-all for the federal government to stick its nose into all sorts of things not covered under the powers explicitly delegated to it, then what was even the point to the Tenth Amendment?