Actually, quite a lot does prevent Americans from moving -- namely the work permits and job offers that are generally required -- just as America limits immigration, so do other countries. I actually have lived and worked in other countries myself, but my employers had to write justifications as to why they were hiring me rather than one of their countrymen.

>Nothing prevents you from moving in a more socialist country.

Countries can control who moves into them, you know.

Language and nationality would be two significant obstacles.