The human right commission elected a Cuban, not Cuba; just as it elected a Lybian woman (from a Muslim state), not Lybia.

The UN is the sole truly international organization, making it possible to communicate with countries from the other side of the world with totally different political systems.
If it were only allowed to states that respect democracy, it would alienate itself a large fraction of the world.
All those politcal systems must co-exist on this planet.
If your nextdoor neighbour throws his trash where he's not supposed to, how can you convince him otherwise?
You need something for all neighbours to rely on, otherwise he'll do with his trash whatever he thinks is most convenient to him.
That "something" is called UN, at the level of countries.

Raoul