Curious, why did you include China as a country you would advise against visiting?
The US State Department regularly issues warnings about travel which you can search by country or region. There are NO warnings regarding China
Alerts and Warnings
Here is the warning on North Korea
Here is one for Iran, but it is mostly targeted at Iranian-Americans
There are warnings or alerts for about 40 nations but none regarding China.
My only concern with visiting China would be poor quality air and water from their lax environmental enforcement because the
decisions to enforce is often made at the local level by boards controlled by industrialists rather than environmental experts.