Definitely think grass should be legal. Don't know much about prostitution.
About hard drugs, if we ever legalize the most deadly drugs, it would have to be something like this:

First make them sit though long classes, informational briefings over a space of weeks. Force them to meet other junkies that are quite far gone. Check out people on withdrawal, maybe even people who die.

Then let them go through a period of preparation, tell all their friends and relatives, say goodbye, put their affairs in order, write a will.

Then pay a lot of money. There has to be a threshhold of pain to make people think twice about it. This also finances the hospital stay.

Then check into a special ward, there's no leaving until either dead or clean.
Here they are kept as healthy as possible, even when they refuse to eat and clean themselves. And the process is slowed down, interspersed with methadone etc. Councellors try to persuade them to quit. If they do decide to quit, there's a scientifically advanced program to help them.

When/if the end comes, it's their choice if they want to see loved ones a final time.