TIL that prostitution was widely legal in the United States up until the early 1900's, when the Woman's Christian Temperance Union lobbied against it. This was the same union that was a driving force behind Prohibition in the 1920's.

Let's go for even more context:

The subject to which the power is next applied, is to commerce 'among the several States.' The word 'among' means intermingled with. A thing which is among others, is intermingled with them. Commerce among the States, cannot stop at the external boundary line of each State, but may be introduced into the interior.

It is not intended to say that these words comprehend that commerce, which is completely internal, which is carried on between man and man in a State, or between different parts of the same State, and which does not extend to or affect other States. Such a power would be inconvenient, and is certainly unnecessary.

Comprehensive as the word 'among' is, it may very properly be restricted to that commerce which concerns more States than one. The phrase is not one which would probably have been selected to indicate the completely interior traffic of a State, because it is not an apt phrase for that purpose; and the enumeration of the particular classes of commerce, to which the power was to be extended, would not have been made, had the intention [22 U.S. 1, 195] been to extend the power to every description. The enumeration presupposes something not enumerated; and that something, if we regard the language or the subject of the sentence, must be the exclusively internal commerce of a State. The genius and character of the whole government seem to be, that its action is to be applied to all the external concerns of the nation, and to those internal concerns which affect the States generally; but not to those which are completely within a particular State, which do not affect other States, and with which it is not necessary to interfere, for the purpose of executing some of the general powers of the government. The completely internal commerce of a State, then, may be considered as reserved for the State itself.

What the court got wrong in Wickard was this:

It is well established by decisions of this Court that the power to regulate commerce includes the power to regulate the prices at which commodities in that commerce are dealt in and practices affecting such prices. [n28] One of the primary purposes of the Act in question was to increase the market price of wheat, and, to that end, to limit the volume thereof that could affect the market. It can hardly be denied that a factor of such volume and variability as home-consumed wheat would have a substantial influence on price and market conditions. This may arise because being in marketable condition such wheat overhangs the market, and, if induced by rising prices, tends to flow into the market and check price increases. But if we assume that it is never marketed, it supplies a need of the man who grew it which would otherwise be reflected by purchases in the open market. Home-grown wheat in this sense competes with wheat in commerce. The stimulation of commerce is a use of the regulatory function quite as definitely as prohibitions or restrictions thereon. This record leaves us in no doubt that Congress [p129] may properly have considered that wheat consumed on the farm where grown, if wholly outside the scheme of regulation, would have a substantial effect in defeating and obstructing its purpose to stimulate trade therein at increased prices.

One man would not have such an impact. It was not even trade between man and man. They assume he would necessarily have to purchase the wheat for use on the market even though that very well may not have be true for him or other cases. And they don't even care if that would be with another man in that state. Just because there is commerce between the states, they say this affects the other states and therefore comes under Congress' power. That's an absurd leap that basically invalidates any limitation on the federal government when they can claim any economic connection.

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