I have (with my own eyes) seen American passports where it is stated clearly on the inside cover that visiting one or more of those (depending upon the year) can lead to
"fines",
"imprisonment", and even
"loss of American citizenship". Those are the ones I've actually seen. I can guess that several more have been added or replaced since then.
I'm sure it's similar to the Berlin Wall where the West stated it was to keep people from escaping and the East said it was to keep people from invading.

So, I'm sure the official Washington line is
"fear of being kidnapped" but your explanation is much more plausible.