FIs, mom and pop shops, middle market firms, whatever, in the realm of free enterprise, should be free to make decisions that aren't using force nor fraud as their North Star. If the marketplace objects to artisans who don't make same-sex wedding cakes, FIs who won't finance Gun companies, or big media firms quashing conservative commentary, those firms will wither. Over time, they die.
That's natural law at work. And until recently, it's how "conservatives" reasoned.
Using the force of government to pick winners regardless of your political persuasion, is what Clinton, Obama, Bidet et al do/did/wish. We can either stay true to principles and pull our business if we object to an FIs decisions, or just make things up to make us feel good like leftist snowflakes.
That libertarian theory of the marketplace would be relevant if we were living in an open, free market. But we aren't.
The theory you are relying on also pre-supposes things like the ability to buy or sell any drug without government intervention, and the right to buy or sell firearms without any government intervention, and the right to operate money transfer and banking businesses without any government regulation.
That is not the world we live in. You are thinking about another world.
As one example, how would a private system of money transfers exist that would enable firearms dealers blocked from using banks to conduct business? It wouldn't because it is illegal to set up money transfer systems which don't meet a large set of federal and state laws and regulations.
In our current situation we have to use the law to shield society from being controlled by large corporations and groups of corporations working in concert with the government.
The reasoning, if not ruling, regarding bakers, was that they could not deny the sale of an existing product/cake. But you couldn’t forcibly commission an original creation.