In the UK you can get on a train without booking a ticket for that train, this is either an open return or just a day pass. The train company has no idea how many seats will be taken or how many people will get on the train. So say it’s a 10 carriage train. Every seat is taken by someone, reserved or unreserved, and theres not a bit of standing room anywhere (this is very common). Which person sat on a reserved red light indicator seat should you kick out? And how do you know they didn’t reserve that seat specifically before you do that? Or do you kick someone specific out of a green lit non-reserved seat, with thier proof that the seat is not reserved and they are allowed to sit there, and your proof that you dont even have that specific seat reserved. It will also be the old people and small children sat down, and you won’t really be popular if you make them stand. Yeah your not sitting if you have this ticket. You’ll likely be stood by the entrance door for 3 hours instead.