Wel, the UN properly shirks from many a 'world law' that would necessarily run afoul of some member-states' sovereign laws, so yes, trying to impose RKBA on other nations is as odious as imposing a universal death-penalty or abortion law on all.
However...
there is PKBA
For example.
We in the Philippines don't have a 2A, but no elected official is crazy enough to propose making firearms-ownership illegal. The **cough** privilege of keeping and bearing arms can be just as useful as a codified 'right'.. (Filipinos can still purchase full auto and hi-cap, though it costs precious money and snail-pace paperwork) particularly when the full weight of a clearly-worded constitutional amendment seems to be less than a guarantee in the US.
Nobody's asking for a universal right-to-own/drive-cars, no?
No need.
But, trying to prevent the outlawing of a privilege/freedom may be do-able.
If so, an international federation of pro-KBA groups would not be without influence in the UN, and usefulness in the world.
h