You buy a ticket, you should be on the flight. No one expects to be tossed out once they are sitting in a plane. What ever happened to the days when airlines announced at the gate they were overbooked and offered first class up grades or free flights for folks who GAVE UP their seats? As a 20 something I did this all the time! It was great! Don’t tell someone they need to leave once on the plane. It is also embarrassing and demeaning.