Try freedom of speech
Sound familiar?
The 1st Ammendment allows people to say (almost) anything without government restriction or punishment for that speech, but it does not protect people from other consequences of that speech. If Ehrlich had the right to hire and fire Smith at his discression, and Smith said something Ehrlich disapproved of, there is nothing in the 1st Ammendment preventing him from firing Smith as a result of that speech.
What would you be saying if Smith had said that called fundamentalists "crazy" or "evil"? Would his firing be justified then?