Many countries manage their own human rights. Why shouldn't we?
We could, but it would depend always on how the individual national government is at managing human rights unless there is an overriding convention holding them to account.
This is why we sign up to international laws and treaties, and work together with other countries, and are not isolationist.
This means that sometimes national governments cannot do everything they want to do politically, particularly when it is against the interests of the human rights of their individual citizens.
Tough cheese. Overriding conventions are far more important than national politics and what fruitbat politicians want to do.
In the 1930 and WW2 we had the likes of Hitler, Mussolini and Stalin "managing their own human rights".
That's why we developed international and European laws and conventions afterwards, so that individual regimes could be held to account.
The threat of the far right is always lurking. Italy has a far right PM. Austria has just elected a far right administration. On the borders of Europe we have dictators and countries that are very far from democratic and liberal.
We need national governments to be held to account more than ever.