Oh, I've heard about that law in Sweden! It's very interesting. 🙂 Hope this isn't too off topic, but I don't know much about what the effects of that law. Does it reduce the levels of violence against sex workers or forced sex trafficking?
With drugs, I think it's a slightly different story because the people who buy drugs are not necessarily the "weak" party, and the people who sell drugs are not necessarily the "strong" party. I'm no drug policy expert, but the situation you are proposing kind of reminds me that of this one statistic, about how in the U.S. there are far more black people incarcerated for drug-related crimes when white people are the top drug users/buyers. How there are levels of racism, classism, etc. that intersect with who is buying drugs and who is driven or influenced to supply it, and maybe a policy like that woudl disproportionately target certain communities that are already hurting from drug abuse, drug dealing and gang violence?
Again, I'm not a drug policy expert and I'm certainly not familiar with the situation in other countries, but in the U.S. the drug war is so mired in race and class issues that it's difficult to extricate it from a more general problem of drug abuse.