But that doesn't work, and leads to all the abuses and downsides of the War on Drugs, like encouraging and enabling organized crime, etc.
Alcohol and nicotine are some of the most addictive drugs out there, and yet we don't jail people for distributing or producing those.
Food is also highly addictive and there's a huge obesity epidemic in the US, and yet no one is suggesting imposing jail terms on the companies that make food or entice people to eat it.
Skydiving and other extreme sports are often described as highly addictive and are obviously dangerous, yet no one is trying to prohibit them. It's widely recognized that if people want to engage in those risky activities and other people want to provide them, it's a matter best left to the consenting adults engaging in those activities -- with perhaps some regulation to help make them as safe as possible.
They are regulated to an extent. You will get fined for selling to minors, for example. Same for smuggling cigarettes and alcohol. And for misleading advertisements and fake medical research. I don't think those fines go far enough.
> Skydiving and other extreme sports are often described as highly addictive and are obviously dangerous, yet no one is trying to prohibit them.
I'm not sure "highly addictive" works here. Do you have withdrawal symptoms if you stop? Does it make you unable to function and think clearly for a while? Is your judgement affected enough that you'd harm yourself or someone else to participate in the sport again? This is a "fun hobby" that will make you sad if you don't do it again, not addiction.
Legalization does not mean lack of any regulation. Alcohol and nicotine, which are legal, are regulated, as you point out. So are prescription (and even non-prescription) drugs. I am not opposed to forbidding sale of legal drugs to minors, though it's not perfectly clear cut (the age limit is particularly tricky to set, and often minors manage to get their hands on alcohol, nicotine, and other drugs anyway).
"Do you have withdrawal symptoms if you stop [skydiving]?"
Actually, I have read of people who did feel like their depression was alleviated through participation in extreme sports like skydiving,[1] and who feel depressed if they don't go again for extended periods of time. So I think a psychological addiction (much like addiction to food where similar effects are seen) can apply.
"Does it make you unable to function and think clearly for a while? Is your judgement affected enough that you'd harm yourself or someone else to participate in the sport again?"
Depression can affect your thought process, and can lead to harm of self or others, so yes, I think those are real risks of quitting for some people who get relief from depression through participation in extreme sports (or other perfectly legal activities which either help them to cope or alleviate their depression).
[1] - "Skydiving Cured My Depression" - https://news.ycombinator.com/item?id=16837748
Heavy addiction: you have X problems, you escape via addiction, now you have X+addiction problems, you stop, you still have X+addiction+withdrawal.
Hobby: you have X problems, you find something that helps you with depression, you have X-1 problems, you stop, you have X problems again.
Most people would not even seriously consider making extreme sports illegal, despite their danger and potential addictiveness, but it's those very same properties of some illegal drugs that are most frequently cited as the primary reasons for making them illegal.
If those are honestly the main reasons that so many drugs are illegal, then why not make extreme sports illegal as well, for those very same reasons?
Nicotine alone is not actually that addictive. I use it as a nootropic and have not seen any signs of getting addicted. Yet years ago I struggled to give up smoking.
With pure nicotine I simply forget to use it for weeks at a time in spite of the large benefits I personally get from using it to aid hard thinking.
Some more here https://www.gwern.net/Nicotine
There are many other substances in tobacco smoke other than nicotine that seem to be far more addictive. Add on the reinforcement from the smell/taste and handling the cigarette and it is a different beast.
We can still jail people actively distributing/producing highly addictive drugs, while at the same time giving mostly free choice and helping rather than harming (potential) users. Monitoring actual results in the society can affect the thresholds of what's done.