In a U.S. context, it is actually really simple. Racism and the age old practice of othering types of people by associating them with a drug (cocaine = rich and white, crack = poor, black and dangerous). That’s it, the full answer is of course a lot more complicated but in the end it is exactly still this dumb and cruel.

politicians across the political divide spent much of the 20th century using marijuana as a means of dividing America. By painting the drug as a scourge from south of the border to a “jazz drug” to the corruptive intoxicant of choice for beatniks and hippies, marijuana as a drug and the laws that sought to control it played on some of America’s worst tendencies around race, ethnicity, civil disobedience, and otherness.

https://www.brookings.edu/articles/marijuanas-racist-history-shows-the-need-for-comprehensive-drug-reform/

I actually think examining the rise of crack in the US and how it was used as a political wedge and xenophobic tool of fear mongering helps explain why marijuana is illegal in the US the easiest, because the forces and structures are the same for crack being highly illegal as they are for marijuana, just much less thinly veiled and dialed up to 11.

They tried to make it illegal and the results were disastrous, one could argue the same for marijuana but the campaign to keep it illegal was much more successful.

Well, there was this one time when we tried out the whole "making alcohol illegal" thing and it worked out about as well as the current "war on drugs." Just like drugs are winning, alcohol won.

The first anti-drug laws weren't really on the books until Nixon, who definitely used them as a way to pin down and criminalize parts of society he deemed unworthy.

July 1971 was when Drug Prohibition started. Before that, technically everything was legal.

Tradition, mainly. It's so ingrained in the majority of cultures that you can't simply uproot it with a law. Although it should be a more controlled substance, no doubt about that. It's addictive, debilitating, incredibly harmful and it simply destroys more lives than literally any drug known to man.

marijuana's prohibition in the US wasn't about reducing harm, it was entirely based on attacking minorities and hippies.

Going to try to give you a clear, concise summary, since a lot of these answers are either too specific or blatantly unhelpful.

First, alcohol has been used by humans since before recorded history. It was probably the first drug we ever used, and barley was even used as a currency in ancient Mesopotamia. Alcohol is ingrained in almost every human society, and banning it is always difficult. The United States actually made alcohol illegal between 1920 and 1933, and it was an unmitigated disaster.

Second, Marijuana wasn't always illegal in the United States. To give you a very oversimplified summary, the newspaper magnate William Randolph Hearst ran a racist, xenophobic campaign to vilify Marijuana in the early '30s. He saw hemp crops as a threat to his holdings in the lumber and paper industry, so he had his newspapers run exaggerated or false stories about crime and violence related to Marijuana use, usually center around Mexicans or black Americans. The movie Reefer Madness is a great example of this kind of propaganda. Marijuana was eventually made illegal in 1937, and as the War on Drugs ramped up over the decades, enforcement and penalties for Marijuana crimes only got worse.

Anyway, there's a ton more that could be said about Prohibition, pre-Hurst Marijuana use, and the War on Drugs, but those are the broad strokes. Hope that helps.

This is a non-US perspective, but my take is this:

Alcohol production has a long and rich history. Many cultures, in particular western, have their own relationships to alcohol. The development of different alcohol production processes tells a lot about the history of a culture.

Belgian monks with their beer brewing styles. Scotch whiskey. French wine yards. Even Japanese with their sake.

Remove wine from France, and we will have another French Revolution with guillotines again. It’s difficult to remove something that’s so heavily ingrained in the culture without public outrage. Alcohol is part of the identity.

Few cultures have marijuana as part of their identity, hence it’s easier to ban.

Part of it also is that it's entrenched in virtually all human societies and history. There's even archeological evidence to support the theory that humans only started settling down to slow them to make more and better beer, count the beer, protect the beer, and tax the beer. They even made bread for the explicit purpose of making beer out of it.

Alcohols cultural and historical position in society

They wanted an excuse to lock up people of color and disrupt communities. With the civil rights act, they couldn’t go old school. So they invented the “war” on drugs specifically because blacks and Latinos were stereotyped as being cannabis smokers. This is all about racism.

Unlike marijuana, alcohol has been an important part of (the western) society for thousands of years. And the last time we tried banning it, it didn't go too well.

They tried prohibition, didn't work.

The way I see it: Alcohol is an older drug, it was engrained in society. But the new drug marijuana could be cracked down on. Also because it was hippies that smoked marijuana, but everyone drank alcohol.

*Lock Stock had a scene. "Want a tug on that? [joint]". Reply: "No I don't want any of that horrible shit. Can we go get drunk now?"

A bit of perspective: During the prohibition in the USA, both cocaine and heroin were sold legally over the counter.

Most illegal drugs today are perfectly legal when a pharmaceutical company produces it and you are purchasing it through channels where the elite gets paid.

I'd say for two reasons. First, laws are written by a bunch of old people (at least in the head) that love the stuff. Second, full prohibition does not work anyway.

Racism is the short answer believe it or not

The other answers mostly sum it up - it was initially made illegal primarily as a way to establish an "other" with which to frighten conservatives.

There's another thing that hasn't been mentioned yet though that I've long thought is relevant - is part of the reason that marijuana specifically was for so long (and still is in some quarters) so condemned.

Imagine you're a corrupt politician, and you want to sell your constituents on the idea of going to war in the Middle East (so you can collect some bribes from defense contractors and oil companies) or instituting mandatory sentencing (so you can collect some bribes from prison contractors) or cutting taxes on the wealthy (so you can collect bribes from rich people and corporations) or any of the other, similar things that corrupt politicians want to do

Who would you rather try selling that idea to? A bunch of pot smokers or a bunch of drinkers?

I think part of the issue is that marijuana appeals to a part of the population that really is, to corrupt politicians and their cronies and patrons, "undesirable." When they want to get the people all fired up in support of their latest bullshit, they want somebody with a beer in their hand, drunkenly shouting, "Yeah! Kick their asses!" Not somebody with a joint in their hand, muzzily saying, "Hold on a minute - you want to do what?"

Something about the timber industry

The US tried to ban it and it just led to gangs becoming super powerful because they sold people illegal alcohol.

So it's not really a policy choice like "this is safe enough, this is not safe enough" it's legal because making it illegal doesn't work.

You can't make cheaper paper with alcohol.

Two things really.

1. Tradition. Alcohol has a long history in European culture and by immigration the United States. It's common to have a glass of wine or a beer with dinner, the rich will impress their friends with the extravagant alcohol they drink serve, you take a glass of wine at communion... heck at one point weak beers were drunk more than water, because at the time nobody knew what made water safe to drink but everyone could tell if beer smelled rotten.

2. Production. Marijuana is easy to grow, but it takes a lot of time and space to produce. Alcohol on the other hand you need something with sugar and some yeast or starter. It can be fermented in some corner of the basement or even a cupboard. It's so hard to control the production of alcohol even in prisons there's usually somebody fermenting pruno somewhere and that's one of the most controlled and monitored environments. It's really hard to prevent people from brewing some form of alcohol because it's about as easy as making bread.

When you combine these two you end up with the disaster that occurred when the United States tried to ban alcohol during prohibition. An easy to produce intoxicant with a large market was suddenly banned, when people started looking for more organized crime stepped in to fill the void.

Because so many people are addicted to it, even the lawmakers are addicted to it. And as other commenters have said, we tried prohibition in the past and it did not work. Society lost their collective minds.

Because you're not voting in the right people.

Years and years and years of lobbying. Also taxes.

I have one word for you, OP: Racism.

The marijuana tax stamp law was put in place because American politicians and voters didn't like black and Mexican people. At the time, it was primarily used by those demographics. Now, of course, it's used pretty equally by everyone.