And on topic of trade union: we are now 20 or 30 years beyond that point depending which treaty you take. When you integrate trade, you agree on rules. When you establish rules, you need a government body. When you govern the four freedoms, how much is left you do not govern. The deeper you integrate trade, the more it becomes a single construct/country/union.

Everything else is just not logically (take international trade agreement eg. US/EU agreements... These are pseudo laws which have such a worse standing everywhere... That is so much worse)