> Is it really the case that there's an argument that this can't work in the US because there are more people?
The simplest such argument would be that there are diseconomies of scale - it's conceivable that the bigger you make a bureaucracy the less responsive/effective/efficient it gets. That certainly could be true - whether it actually is is an empirical question.
Another possibility is that our federal system is ill-suited to the task. There's nothing really preventing individual US states from providing such services. And if most states haven't done so thus far - and in the few that have tried, it hasn't worked out very well - there might be reasons for that which we should try to understand.
Many individual US states are larger than individual European countries. People can immigrate within the EU, can they not? So why defend the UK or Denmark having its own system?
On the other hand, it could easily be argued that interstate commerce restrictions are a big part of the problem in the US. Suppose some company in Delaware comes up with a really cheap health insurance plan that meets my exact needs - I can't sign up for it, because I don't live in Delaware. For a company to offer health insurance or health care nationwide it has to have offices in 50 states and navigate regulatory restrictions in 50 states.
If McDonald's wants to expand to serve people in other states, they can just DO it, but Kaiser or Blue Cross can't do the same. That situation is ridiculous and needs to be fixed somehow, but I don't hold out much hope for it changing any time soon.
The simplest such argument would be that there are diseconomies of scale - it's conceivable that the bigger you make a bureaucracy the less responsive/effective/efficient it gets. That certainly could be true - whether it actually is is an empirical question.
Another possibility is that our federal system is ill-suited to the task. There's nothing really preventing individual US states from providing such services. And if most states haven't done so thus far - and in the few that have tried, it hasn't worked out very well - there might be reasons for that which we should try to understand.