Why is trading good for both people or groups involved?

Both sides get something out of it. If people are trading it is likely they are trading for something they don't have direct access to and therefore need to trade something for it so someone else can give it to them. If the trade is fair, both sides are happy and satisfied with the item(s) they received.

- "schenck v. united states, case in which the u.s. supreme court ruled on march 3, 1919, that the freedom of speech protection afforded in the u.s. constitution's first amendment could be restricted if the words spoken or printed represented to society a “clear and present danger.” "

- speech aimed to potentially create danger could be banned.

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