An American tourist? I'd need a passport for many other locations, unless you're talking about the Bahamas. It's really, really easy to travel to Puerto Rico.
For foreigners, I understand it's probably easier to enter any of the other sovereign islands than a US territory, or (if you're from the EU), any of the colonial islands would also be easy.
I'm not sure what the parent is referring to. If you're an American citizen, you don't need a passport, just book a flight. Large numbers of the population speak English, and much of the US is already there. The roads are the same, the dollars are the same, hell, even the fast-food is the same.
Yes knowing what side of the road to drive on and understanding driving laws and being able to spend the currency you already have are indeed features.
As a European not belonging to VWP you have to go through the process as if you were going to mainland US which is ridiculous. All neighbouring islands I can visit with visa on arrival - don't have to go to any embassy to beg for the privilege to visit your country.
For foreigners, I understand it's probably easier to enter any of the other sovereign islands than a US territory, or (if you're from the EU), any of the colonial islands would also be easy.