Moral framework:Individuals probably have freedom. This is affirmed by various ethical philosophies (freedom is essential to living a happy, utilitarian life; violating freedom is a non-universalizable act and thus un-Kantian; respecting other people's decisions is kind and virtuous in a way that would satisfy Aristotle; etc.).
It is my opinion that freedoms are inviolable side constraints, that is, no person or government should unconsensually limit a persons freedom, even if for a good purpose. This is for a variety of reasons - I think deontology agrees with this; argumentation ethics; and some a priori arguments for the importance of freedom and absolute moral worth of each person. And to be more nuanced, I take the approach that each individual owns him/herself, and by extension decides what to do with him/herself.
Thus, I am of the belief that an individual can do whatever he wish so long as he or she does not encroach upon the ability of others to do that. This entails doing drugs, or prostitution, or any other behavior that is in the status quo illegal despite not violating anyones self-ownership.
Keep in mind that this doesn't entail neglecting regulation. Regulation is essential to protecting individuals rights and self-ownership. For example, prostitution is consensual, but human trafficking, rape, and other crimes associated with prostitution clearly violate freedom and an individuals rights. Those should be prevented. This actually supports legalization of "victimless" crimes, because when they're legal, they can actually be safely regulated.
My framework is also non-consequentialist, so even if legalization of drugs harmed society or the economy, I would still support it. But, even if consequentialism is true, and even if it is possible to evaluate consequences (I believe consequences are largely impossible to evaluate), legalization would still be beneficial.
Net benefits of legalization:
Firstly, I'd argue that legalization decreases drug usage.
The trend of current legal drugs like tobacco and alcohol is actually DECREASING usage, because of smart education (2).
Historically, alcohol prohibition goes to show how ineffective our current drug prohibition probably is.
Desensationalizing drugs is key to decreasing their popularity.
Additionally, legalization saves lives. Tobacco and alcohol are deadlier than many currently illegal drugs. We'd prefer for drug addicts to be hooked to marijuana rather than alcohol (1). Drug deaths are also mostly caused by lack of safe regulation, what Ostrowski calls "black market factors (1). The actual drug rarely causes the death. If we were to create a safe, legal setting for drug usage, deaths would decrease.