Surely this isn't as difficult to understand as some people are trying to make out.
If there is a genuine safety reason (broken seat, last minute need to add fuel for changing Wx and now above MTOW or whatever), the PIC has legitimate authority to request a pax to get off). 99% of pax will get that. Hopefully the carrier will compensate the pax for something which is really no ones fault but rather circumstances beyond everyone's control. Next possible flight, lounge access, upgrade .....whatever. Isn't that what most of us would expect if we drew the short straw for the greater good? This safety reason separates airlines from other businesses like restaurants or cinemas or whatever.
LEO have dragged pax off for legitimate reason - intoxicated or whatever. And the other pax support that and won't come to the defence of the clown. The fact the video shows outraged pax (some of whom allegedly subsequently refused to reboard) should be a hint that this was not right.
Could a hotel or cinema or restaurant demand someone vacate so an employee could take their place? Of course not - it's not safety related. So why should an airline?
The fact some people still don't seem to get this is the centre of the pupil of the bullseye of the failed customer service culture that so many pax have experienced.