… is from chapter 3 of William Graham Sumner’s 1885 book, Protectionism: the -ism Which Teaches that Waste Makes Wealth  (original emphasis; footnote omitted):
Trade is a beneficent thing. It does not need any regulation or restraint. There is no point at which it begins to be dangerous. It is mutually beneficent. If it ceases to be so, it ceases entirely, because he who no longer gains by it will no longer carry it on.