It is a bit rich that if a communist dictatorship and a former communist dictatorship (now authoritarian semi-dictatorship) gives their OK to democratic countries to wage war it's OK but if they don't it's against international law.
China and Russia are not well placed to be moral authorities on justice and human rights so why should the USA listen to them?
I don't support the current US foreign policy but I find it hard to listen to people holding up the UN as an example of all things shiny and righteous.
The Chinese are making too much money supplying arms to the Sudanese government to do much about Dar Fur.
The UN's record on supporting the good guys is deplorable.
Remember that they did nothing in Rwanda except send in French troops to support the genocidal Hutu power government and actively help to kill 100,000 people within their "zone turquoise" in the time they were there.
Then after the rebels stopped the massacre the UN sent nothing to the survivors but sent tens of millions to help 90,000 or so murders in the Congolese refugee camps.
We had the biggest concentration of mass murderers in one place in history and all the UN did was give them food and money to continue the genocide (an additional 20,000 people were killed in Rwanda by gangs based in UN run Congolese camps after the war was over. This only ended when the Rwandans invaded the Congo and overthrew it's dictatorial government).
And it's still going on, see
herefor details.
The UN, at a security council level, is a farce.