Sweden has probably just recognized that prostitution and it's side effects is a simple demand-side problem of a market. Legalizing consumption drives up the demand because more consumers do it and it also attracts consumers from outside the country. Plus there's increased human trafficking for sex work because that demand has to be fulfilled to make money in the market. So prohibiting consumption is the easiest fix to the problem.

1) There is no evidence of that legal prostitution anyhow leads to the human trafficking. 2) Prohibiting something is not the easiest fix to the problem, because of it does not fix the problem. More correct to say - there is no problem to fix.

@Draif Kroneg: Note that all this is immaterial to this question, which is not “What is the best way for a country to deal with prostitution?” or similar. However, I don’t think you have properly understood the point of view that is prevailing in Sweden: It is not just about human trafficking or force; prostitutes who have decided themselves to work in this “industry” are also considered in (psychological) danger.

The question originally included drugs as well - does the same apply in Sweden in that situation, i.e. "drugs are harmful, so we can't allow people to make that decision for themselves"?

@janh: Yes – trade, possession and use of most drugs is a crime in Sweden (with the common exceptions of alcohol and nicotine). So the situation is somewhat similar, except that this policy on drugs is more widespread globally than the Swedish asymmetrical policy on prostitution.

@DraifKroneg Why don't you give scientific sources supporting your position?

@chirlu My question was (sort of): If the rationale behind the law in Sweden is to protect the prostitutes and society, why not prohibit prostitutes from offering themselves also to keep them from harming themselves?

@janh because of it is impossible to prove the absence of the proof. Just like there is no trustable scientific evidence there is pink unicorn on the moon - there is also no trusted scientific evidence the prostitution aids human trafficking. If that would true - most western countries would strictly ban it.

@DraifKroneg wrong, it's possible to show tha there is or there's no correlation between legalized prostitution and trafficking - and you failed to show evidence supporting either option. While you are right about "proving the absence of proof" in strictly mathematical sense, it's not really relevant, as you can't "prove" anything in social sciences like you would prove eg. that set of prime numbers is infinite.

Related question on Skeptics.

@el.pescado You could probably prove many things in the social sciences, but we cannot do certain experiments because those would be considered inhumane. If DraifKroneg still insisted on a proof, well, what then...

@jjack probably because if you make prostituting yourself illegal, and someone forces you to prostitute yourself, it's even harder to inform the police because you'll go to jail yourself.

@Erik True, but that would make you a victim, not a criminal. But I can imagine this to be a bit much to consider for sometime who's under intense pressure.

@jjack you're only a victim if you can prove it. You´ll be in one of those "guilty until proven innocent" situations if you admit to a crime and then try to show that you had no choice but to do it, and that's a bad place to be in.

imgur.com/a/wz4Cl I've added some reference for germany. You can see a correlation, but a much stronger correlation is with the addition of Romania and Bulgaria to the EU. However: 14 years after legalization, case numbers are back to pre-legalization levels. Imho, prostitution and drugs are very related in that if you outlaw it, you a) create a market for organized crime, b) loose your ability to control and influence it and c) won't achieve a lasting effect.

@jack: Quite obviously Sweden doesn't think they have the right to prevent a woman from doing something that might be harmful to herself. As you say, it's a liberal country. They think they have the right to prevent other people from doing something harmful to her or to society. They are liberal, but not stupid.

@gnasher729 If the police arrives before someone can kill herself, they take the person to the hospital. So obviously the state thinks it has the right to do this. I doubt Swedish police would leave and say "ok, it's your free will, take it easy".

@jjack : Bringing a person to the hospital is something very different than putting a person in prison and doesn't happen under laws that forbid something.