I agree with you on moral grounds, but technically human or natural rights are not the same as legal rights. In particular, they cannot be guaranteed by any document the UN produces, unless embodied as legal rights within a functioning judicial system. Instead, these rights are more like ideals.
The US did sign this as a treaty. But yes that is why in Europe most of these rights were signed into law as the European Convention on Human Rights, which adds a court to enforce them. They did remove some like the right to democracy, bizarrely.
