This is one of the more persistent, retarded commie/socialist arguments and it's fucking dumb.
It's basically "socialist countries are sabotaged from the outside".
But it's absolutely a legitimate point of criticism to analyze any individual system for its viability in a hostile environment.
A nation might be internally socialist, which is fine but it's totally a fair point to analyze how it fares internationally. Among independent nations, that's effectively a free market naturally. There's no global world regulatory power (I know they try to establish one but the results have been mixed, to say the least), so your country trades with whoever will have you. It's almost the freest market.
So you can totally go as socialist you want. That's fine. But you need to be able to hack it on an international level.
And in fact, there absolutely are some mixed socialist economies that survive just fine. Scandi countries do well. But they
have a bizarre ant colony culture that I don't fully understand.
That would not work in a nation of trailer parks and housing projects. An
yone who thinks they can bring socialism to America is retarded.