Prohibition
Prohibition proved, among many other things, how stubborn Americans are about things they feel they need. I have used prohibition to counter many arguments; some people say that we should make cigarettes illegal, abortion illegal, etc. Though I agree with them in many cases that the things they are talking about are not inherently good, prohibition proves that making that thing illegal will cause far greater damage than just educating people better on it. For example, abortions happen now. They are, for the most part, done out of necessity; they are done to be safe for the mother and to cost a relatively low amount. But, if we make abortion illegal, they will still happen: just by sketchy doctors, charging too much for the people getting them and likely hurting the mother severely in the process. (Just like Moonshine causes paralysis, blindness and impaired neural function, while alcohol itself, in the same amounts, just makes you act unlike yourself.)
This event has affected our freedoms today outrageously; now the government knows not to outright ban something addictive that is in high demand, for a disproportionately bad consequence would most definitely occur. America is known for our freedom, and we fight for it in this way.