But again, the fact is that we can openly have, and pursue aggressively, discussion about and attempts at reform around how this is handled.
In fact we see this by the spread of various drug legalization efforts in the U.S. and efforts at prison reform.
Though there is also a huge difference between a governments authority to regulate the distribution and consumption of psychoactive compounds (and/or the sale of such compounds) and the ability to even discuss how the government is handling the issue.
Free speech and criticism of the government are a bare minimum baseline. So you can actively organize your fellow citizens in an effort to legalize various compounds in the US and you can lobby and protest the government without any fear of being arrested because of what you are saying. That is a completely different world than what goes on in China. If you are a dissident you are a criminal.
And with respect to whether or not the UN could openly address internal affairs of the U.S. - well it does: https://undocs.org/A/HRC/38/33/ADD.1
Yes the U.S. ambassador to the UN had some choice words about that specific report but it was all out in the open and wasn't suppressed