Player's have every right to PRIVATELY hate AMERICA.  (And WE have an equal right to hold them accountable for that 'hate'.)...  What they do publicly however, is expected to fall within accepted 'Societal Norms' and to be Lawful.  This where miscreants like BLM and ANTIFA get a huge "Yellow Flag".  And NFL 'kneelers' behavior becomes 'questionable', at least to most ...  BUT, what you can and can't do 'at work' is heavily restricted to following the employers' stated 'rules and requirements'. This is where the NFL 'kneelers' are both 'out of bounds' and 'yellow flagged'...  In other words=> YES. The Constitution absolutely protects your 'Personal Rights'.  BUT... NO, it does NOT give everyone the 'right' to do anything they want, anywhere they want, anytime they want.