I never understand how people point to existing systems that are working for a country, and then make the (valid) point that the success of those policies can't necessarily be extrapolated to another country, but then (invalidly) believe that is a suficient statement to end the conversation.

Especially because those people often are talking about countries with some form of democratic socialism (where there are a number of strong success cases), and instead frequently put forward libertarianism - which is a completely untested government form in any country.