Earlier quoted context omitted.
It seems like you should just be comparing pre-tax salary converted into the same currency?
Not really, for example in France I can go and do a full-spectrum healthcare check (eyes, dental, physical, mental, name it...) and it would cost me -in total- less than 100€ nothing is deduced from my salary. One year of prestigious university is less than 600€ in fees... Cost of living, education, transportation, etc... also are a factor.
I mean sure, France's government and health care system is probably a bit more efficient than America's, but I doubt it's order of magnitude different. Maybe more importantly, but in the other direction, as a developer in France you're probably paying more for healthcare than you use (subsidizing the average person who pays less taxes). Quite arguably differences like those are things that you are purchasing with your salary by choosing to live in the US instead of France, I don't think it's either desirable or really possible to eliminate them.