As a frequent pax this discussion is somewhat disquieting - what with all of the I'm the captain and I'll decide who flys rhetoric. Of course the captain has the ultimate authority on board but that is not freedom to eject anyone because their race disturbs crew or other pax. All the lamenting about the flight crew being held responsible if something going wrong - who cares - do your job the best you can and deal with the consequences - happens every day in this mixed up world. As the comments about instant offloading of pax who are not following flight crew instructions or argumentative - you have to be careful to apply reason here. If the pax is interfering with crew, safety or operation of the aircraft by all means show them the door - use the toe of you boot if needed - but remember some people who appear to be problems may not understand, may not travel regularly or may just be trying to express a legitimate complaint.