(like the US, the worst human rights violator on the planet)

You're being far too dramatic. The United States doesn't have a good human rights standard. One only needs to look at the prison at Guantanamo Bay, or the U.S. Prison System but it's no where near as bad as Saudi Arabia, or North Korea, or Israel, or Iraq or Syria (Bashar al Assad is murdering his own people. Is that defined as Human Rights??), or Egypt (go research how Egypt silences dissent or activism), or Bahrain (look up Nabeel Rajab, or Abdulhabi Al Kawaja and his daughters Maryam and Zainab...all human rights activists).

The reason that the UNHRC exists isn't because of US, Israel, Russia, or China. It's because international treaties and conventions which protect the human rights of all persons exist and have been signed by most of the UN member countries. The UNHRC's job is to monitor the human rights conditions of countries that are obligated to abide by the treaties and conventions that they signed. It's why the OHCHR conducts an annual review of the member countries. The fact that Saudi Arabia, which is actually one of the greatest violators of human rights in the world, has a seat at the UNHRC shows that the system is thoroughly fucked up.