People (this author included) seem to forget the vastness of America's size and the depth of it's diversity. People and society in San Francisco are nothing like that of Birmingham Alabama or Fargo North Dakota.
Seems to me like stereotypes and generalizations being leveraged for views/clicks.
The smells, the noise, the mental deterioration. The shear amount of people that just resign to the world in big cities---and San Francisco in particular---is more than an order of magnitude greater than anything you'll find east of the Rockies and west of Chicago.
The comparisons the author makes are on a scale much larger than the diversity of the USA.
If you cannot see this I cannot work out how to tell you, except perhaps to suggest that you and live and work on the other side of the world.
don't understand your last sentence. been in china/hk, there's a lot less diversity there, at least racially. are you using diverse in economic terms? gender? age? consumer habits? religion?
This does not require the destination to be diverse, simply very different from the USA.
Have you travelled outside of the major cities, or even > 50 mi away from an international airport? I've been traveling the country for a living for the last 15 years and the diversity is staggering.
If the USA is so homogeneous, what nation on this planet would you consider more diverse?