The players are employees.  The CBA dictates whether the owners have the authority to compel the players to stand.  At our firm, if an employee chooses to protest a political stance in the workplace, it is their choice.  If it is in bad taste or results in a loss of perceived reputation of the firm, we will fire them with cause.  The point is to protest on your own time, not on your employer's.  It's really that simple.