@ RealLifeDad (RLD)
To answer RLD's question, I am not really sure on what Dr. Paul's thinking is on "the right of business owners to decline service at will", per his son, Sen. Rand Paul's remarks.
At a purely libertarian level, there should not be any real issue with this - since doing business between two parties implies a willingness and a trust between the two parties to exchange goods and services for some legal tender or other money with value to both parties.
Of course, the very fabric of modern American politics is deeply dyed with concerns of race, ethnicity, religious affiliation, and most recently, sexual orientation and gender identity, on top of a multi-generationally entrenched, and federally (if not backed up by state statutes) enforced "fairness".
To be perceived as speaking unfavourably of these laws and statutes and court precedents is to touch a "third rail" in politics at the very least. No matter what Sen. Rand Paul's (or that particular poster here) intention (which I believe on the face of their argument to be a defense of free markets and individuals to choose with whom to transact business)... it will be quickly perceived as a racist/sexist/ethnocentric/homophobic/otherwise-bigoted, reactionary remark.
Perceptions are the fly in this ointment: It certainly does not help the Honourable Senator from Kentucky that he is representing a state which was a border state in the war, and whose population was a target of the "Southern Strategy" where perhaps older racial prejudices took a longer time to be dispelled. That is not to say that a similar remark falling from the lips of a senator from a (generally more liberal) northeastern state would be perceived as being any less objectionable, but perhaps people are conditioned to presume that people from Sen. Rand Paul's region (and generation) are more likely to quietly harbour some unpleasant ideas that every once in a rare while bubble up to the surface.
I more or less held my peace when a few particular RJ'ers got into a multi-page heated discussion about that very topic a few weeks ago.
The reason for that is my opinion is not well shaped on this: as to whether or not it is constitutional for a business owner to be "forced" to do business against his will (that is, serve specific persons or groups of people of a particular identity), and the responsibility of government to ensure that the rights of people to do business (primarily referring to the customers here and not business owners on this part) are not infringed.
In the generation or three following that of the Framers, minority rights were largely undiscovered and the rights of businesses and customers to conduct or withhold business was a free market affair - wide, systemic denial of service on account of race and ethnicity would not arise until the first major waves of immigration (first Ireland and then Eastern Europe) followed by the aftermath of War Between the States (the so-called US Civil War of 1861-1865) when the 14th-16th Amendments expanded citizenship and various rights to include the newly emancipated African-American population in the former Confederate States.
The other development is that business has largely migrated from the "Mom and Pop" corner store to the omnipresent nationwide (or truthfully, multi-national) Big Box superstores.
Or other multinational corporations - with whom most Americans must interface with on a regular basis. Choosing to "take your business elsewhere" to punish an offensive business is still an option, but this is much less meaningful than it used to be when the competition was any of a number of similar smaller competing businesses in the same town. To have any sort of effect on such large volume operations, organizing boycotts and demonstrations becomes necessary - something beyond the "care and concern capacity" of most average folks.
For now, I believe that the current body of law as derived from the 14th-16th Amendments and other case law that has been codified to defend minorities from unfair and discriminatory business practices are part of a "necessary lesser evil" until such time that Americans are truly able to look at one another and be truly blind to skin colour, ethnicity, sexual identity, and etc.
But I am also inclined to recognize this "evil necessity" as a small burden that also hobbles the freedom of the market (in purely libertarian terms) to an extent.