I read a fascinating internet article on Prohibition a few years ago which of course I didn't bookmark and can't find now. This is a particularly myth encrusted episode of US history. I will try to summarize the article using points that can be easily verified using Google searches, but there is still a risk of too many heads exploding over this.
1. Prohibition was not particularly popular when it started. The initial strategy of the prohibitionists was to use initiative and referenda to get states to establish prohibition laws. This failed. The public kept voting down prohibition ballot proposals.
2. The constitutional amendment was actually a clever end run over the fact that prohibition was unpopular. Remember, to pass a constitutional amendment you need a supermajority in Congress and to get three fourths of the state legislatures. The public is actually not involved at all, except obviously for electing members of Congress and the state legislatures. But remember the US is not exactly a democracy and was even less so at the time. Legislative districts didn't have equal populations, the franchise was restricted, elections were stolen openly, and this was the period when a political party (the Socialists) was shut down by the police and when Congress blocked the constitutionally mandated re-apportionment of state delegations. So it was perfectly possible to ram an unpopular unconstitutional amendment down the public's throats! The article claims that is what happened.
3. The tactics used to sell prohibition were not on the up-and-up anyway, many supporters assumed that it would just apply to hard liquor, not to beer.
4. The enabling federal legislation went much farther than required by the amendment or on what supporters envisaged, and was more draconian than the rules in other countries where alcohol was prohibited. You couldn't create alchohol solely for export, no exceptions were allowed, it applied to even weak and small quantities of alcohol, etc. The enabling legislation, the Volstead Act, was thorough impractical and unenforceable.
5. Because of # 2 to # 5, many police departments simply refused to enforce the relevant legislation. Remember, police was still an entirely local responsibility. It wasn't that it is easy for people to evade laws, in many localities the local government and local government had no intention of enforcing the law. Eventually in alot of cities you didn't even have "speakeasies", liquor was sold pretty openly.
6. Because local police weren't enforcing the laws, you got a big expansion of federal police power, eg agencies such as the FBI.
7. Prohibition actually grew to be fairly popular as people got used to it. In 1928 there was a presidential election that directly pitted a "dry" candidate, Hoover, against a "wet" candidate, Smtih. Hoover crushed Smith in the voting results, and dries had firm federal legislative majorities throughout the 1920s. The reason the amendment and the Volstead Act were repealed is that the "wet" minority made up an important constituency of the Democratic Party, and when the Democrats swept into power in 1932 due to the Great Depression, repeal of prohibition was almost literally the first thing they did, to reward their base voters.
8. Prohibition meant literally shutting down entire industries and throwing people out of work, something that is often forgotten. The only place where you say anti-free market measures on this scale at the time was in the Soviet Union. Its also no coincidence that the repeal came at the bottom of the Great Depression, the economic crisis was so bad that the country couldn't afford to have entire industries shut down like that, let alone the money poured down the drain with enforcement.
9.. Repeal didn't turn back the clock to the status quo ante legally, which you can see by just reading the text of the two relevant amendments. Regulation of alcohol at the federal and state level was still considerably different (more restrictive) in 1934 as opposed to 1916. And around the same time as prohibition lots of other drugs were banned and remain banned to this day. The big increase in police powers, especially federal police powers, is also still there.
10. Prohibition reduced consumption of alcohol in the US, and the effects lasted for at least decades past the repeal. It also killed the saloon culture of the nineteenth century, which was a key objective of the prohibition. The idea that nice middle class people have a few drinks at the end of the day at home, each day,and don't go to bars is pretty much a prohibition derived idea. Alcoholics Anonymous was founded in the 1930s, and again this wasn't a coincidence.
I will pretty much leave things at there, but the big myth is the idea that Prohibition was some sort of failure. The prohibitionists accomplished most of their objectives. Granted, stopping people from drinking alcohol completely is not possible, Muslims in Muslim countries that have complete bans on alcohol for example drink, they just are careful not to do it in public. But banning public alcohol consumption and public drinking culture is very achievable, and what re-emerged after the repeal of prohibition was very different from American drinking culture in the 19th century. Though variants of the idea were tried pretty much everywhere, American drinking culture is still noticeably different than in the rest of the world. And prohibition brought with it a big expansion of police power.