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."
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.