Economists have long been in love with this simple argument. They have since the eighteenth century taken the argument a crucial and dramatic step further: that is, they have deduced something from it, namely, Free trade is neat.
If each deal between you & the supermarket, and the supermarket & Smith, and Smith & Jones, and so forth is betterment-producing (a little or a lot: we’re not talking quantities here), then (note the “then”: we’re talking deduction here) free trade between the entire body of French people and the entire body of English people is betterment-producing. Therefore (note the “therefore”) free trade between any two groups is neat.
The economist notes that if all trades are voluntary they all have some gain. So free trade in all its forms is neat. For example, a law restricting who can get into the pharmacy business is a bad idea, not neat at all, because free trade is good, so non-free trade is bad. Protection of French workers is bad, because free trade is good. And so forth, to literally thousands of policy conclusions.