I've never understood the criminalisation of drugs. If they were legal and you had to go to a hospital or mediclinic to buy them, then at least tou can ensure thise getting them are is a safe environment with access to care and can be informed constantly of the hazards. It woyld also mean that the money spent on those drugs can be taxed which would theoretically increase the amount of money available to use on the country's needs. Finally it would remove all the income from the criminal drug dealers. If the wanted to continue to deal they would have to go through the regulation channels which would mean it would be very difficult to continue their violent and harmful practices.
A similar argument can be made for legalising prostitution. The only people who benefit from these things being iligal are those whose job it is to catch the individuals breaking the law and those who are at the top of the iligal organisations making the money.
Criminalization is not a rational policy, it is based on emotion and money. However, I think it is safe to say that legalizing prostitution would reduce the income of certain prostitutes. The sex workers I have spoken to seems to want the benefits of legalization but none of the disadvantages (like possible market competition). Now prostitution is often controlled by organizations that decides who will work where, which is very beneficial for certain sex workers that work outside the syndicates in high end-markets.
Imagine for example you are a weed farmer and instead of selling it for 10 EUR per gram you have to sell it for 0.1 EUR per gram or less. Not as fun.
Although it would end up balancing out. Those who aren't happy with the income would leave the industry increasing the low income because theres less supply until those who stay are happy/willing to accept with the income they are earning and at the same time their lives won't be at risk every day.