The concept of "Duty of Care" is not just a British thing. It exists in the USA as well as Europe. It just so happens that in the UK it developed through common law.
The Duty of Care in Irish Tort Law
Duty of Care-Wikipedia
The Captains decision might be final, but he still has to be able to justify his decisions. To the customer, the licence issuer, and his employee. He does not live in some God given bubble. As much as some would like to believe they do.
On the ground, with the doors open, the Captain's decisions are far from final.
@TS re- the deleted post. It was there, I posted, and then looked to check it had been posted. Well I thought I had. It' an age thing.