The only exception should be legal monopolies; they shouldn't be allowed to discriminate, because there are otherwise no other options.
This was not the conclusion of the SCOTUS case.
It pushed the case back down to the State on procedural consideration.
We also have a bunch of reasons (protected classes) that a company cannot refuse to do business. Colorado specifically includes sexual orientation in their definition of protected classes.
I don't think this is relevant to this specific case. The baker didn't refuse to do business with the gay couple. He was happy to sell them a generic off-the-shelf wedding cake.
He refused to sell them a personalized cake, which is considered a form of expression. The government cannot compel you to express yourself a certain way if it goes against your religious beliefs.
If you're talking about the Masterpiece Cakeshop baker, he didn't say that until the lawsuit was in-progress. At the time that the couple went in, he refused to serve them without discussing what they wanted.
I would absolutely support adding sexual orientation to that list in every state, or at the federal level. But if it's not there in the bakers' state, then, legally, they are (unfortunately) in the clear.
So you're fine with "whites only" signs in shops?
Hope that doesn't sound too extreme but while I understand where you're coming from I think it's important to acknowledge where the rhetoric about not distinguishing your customers based on their personal characteristics comes from.
There are a couple cases being heard by the Supreme Court right now that are attempting to argue that discrimination against gay and transgender people is inherently discrimination based on sex (which is a protected class everywhere in the US); I'm very interested in how that turns out.
Anyways I think your point is mainly that there is a line between what is required of a business and what constitutes a right to self-determination / self-expression. Where to draw that line is certainly not obvious and we understand new things about it as society progresses. So in that sense I do understand your point of view, and I happen to agree that certain decisions regarding what work they take should be allowed by a business, but I hope the point has been made that you have to be careful what you wish for when stating absolutes like "for whatever reason they choose."
That's not what the Supreme Court found; it has not invalidated public accommodation anti-discrimination law in general, nor even the specific law the State relied on in the case. It did rule that the specific procedural history of the case indicated that State officials acted with specific targeted religious animus in the case, invalidating the state enforcement action even if the law was Constitutional and the enforcement factually warranted under it otherwise.