It is so fundamental, however, that it remains as invisible as the forest for the trees. It is the matter of jurisdiction. The Constitution is quite clear. It grants Congress jurisdiction in a very limited area, and that means geographic area. A person or group has jurisdiction over that place which is his.
French law applies in France.
You can set a curfew for your children, not your neighbor's children. General Motors employees have to follow GM rules, not those of Ford. This isn't some tortured theory. We have had plenty of those, all of them based upon sincere reasoning and fervently held beliefs, but which appear almost laughable to a jury of men and women who had never thought of these things before. But the Constitution, in language a child could understand, sets the limits of federal jurisdiction, period.