Those other nations have very different setups though. I don't believe anyone thinks it's "impossible, too expensive" as in physically impossible, but rather "impossible to do it and keep the basic setup of the American society as it is".

Of course it's possible for the US to have the same social systems as European nations, but every American would have to pay a lot more taxes. I understand "it's impossible" to mean "it's impossible to do in this configuration". You can build a sky scraper instead of a single family home, but it's impossible to do on the same budget.