I don't see how its acceptable to use coercion to enforce an opinion of "duties that trump free speech rights" that don't involve force, fraud, or defamation.
Doing business thus is validly subject to government regulations mandating that businesses do (or not do) certain things. And some of those things include not discriminating against the disabled, and designing your business facilities to accommodate the disabled.
I also find fault with the commerce clause of the constitution and think its broad interpretation as an economic defense mechanism is archaic and filled with undesirable effects (such as the drug war, limitations to trade and international tariff wars), not to mention contradictory to the constitutional principle of liberty.
The Constitution was intended to give the government broad powers. It was written in reaction to the Articles of Confederation, which created a government with limited powers that failed with 5 years. The provisions of the Constitution and the bill of Rights need to be understood within that context.
"The United States Constitution presents an example of the federal government not possessing any power except what is delegated to it by the Constitution — with the Tenth Amendment to the United States Constitution making explicit that powers not specifically delegated to the federal government are reserved for the people and the states."