Colonialism

I aware of the facts - but again, at the national level obedience to international law is voluntarily. If Britain decides not to accept that decision then Britain does not accept that decision.

Especially in this case.

To quote:
"In 2019, the International Court of Justice (ICJ) issued a non-binding advisory opinion stating that the UK "...has an obligation to bring to an end its administration of the Chagos Archipelago as rapidly as possible, and that all Member States must co-operate with the United Nations to complete the decolonization of Mauritius".

Non-binding, advisory, means that the British and the Americans can ignore it.

What happened in 1960s was against the principles of the UN - but legal under UK Law.

Many, many things happened in the 20th (sorry about the mistake above) century that we look at and say "But that was illegal".
Examples:
The cleansing of ethnic Germans from Prussia and other central European nations.
The actions of the USSR in the Warsaw Pact nations.
The racially based laws in South Africa.
The repression of black voters in the US.
"Indian" Residential schools in Canada and the US.

Were any of these things right? Should any of them been done? No, but they were legal under the various national laws of the day.

Looking at the Islands today, the UK has not rectified an historic wrong. A wrong that can't be righted with a stroke of a pen. No, it would be a messy can of worms.

Would the Mauritius government have to repay the 3.66 million pounds (plus interest) that it received? Would the plantation owners be given back their land? Who qualifies as natives of the Chagos Island? Would the US decide to respect that decision or insist that their lease is a valid one?

The US handling of Guantanamo Bay suggests the US will be there at least until 2036.

But you know what would make sense? If we could go back in time and spank everyone who was involved the decision.

Certainly is - and often well beyond 'silly'. A glorious example yesterday from Sir Lindsay Hoyle, Speaker of the House of Commons, who described the Queen's funeral as "the most important event the world will ever see."

Hoyle's well-known to be a tetotaller - so he can't even claim to have been drunk....

Well, there are other possible explanations. Does he smoke crack?

Not that I'd heard of - but maybe....