The number of drugs who are linked to a higher chance of criminal behavior due to being intoxicated are rather limited and when it comes to drug related crimes another topic in itself.
Someone smoking tobacco, weed or heroin wont just suddenly get the idea, that it would be fun to rob someone.
When it comes to heroin, but also other highly addictive substances, the main issue is procurement crime. Which is no wonder if someone is addicted and you look at the street prices. Its not feasible for alot of people to make that kind of money legally. Which is a completely different picture if you look at procurement closer to production cost. Production of something like poppies is as inexpensive as it gets.
Cheaper drugs will likely reduce theft and gang violence, but they sure as hell won't prevent people from being irresponsible while intoxicated.