

I agree with your first point, but it’s not the main reason why US was attacked - even if it was 100% isolationist, it would have been attacked anyway, because Japan can’t really fulfill its imperial ambitions, if they have the US pacific fleet in its backside.
For normal people, the fee for non-residents would be something like 50chf a month. For americans, I imagine it would be way more to comply with the US banking secrecy laws.