Unless administered by the government drug use, in the common parlance, isn't government experimentation of peoples' lives. People are experimenting with their own lives when taking drugs/narcotics.
The reasons to decriminalize drugs, or not, from a government perspective is policy that can be typically measured as cold numbers. Such numbers can include:
* cost of drug treatment / rehabilitation
* cost of lost/missing work
* decreases in numbers of incarceration
* changes in traffic fatalities
* changes in rates/frequencies of drug consumption
Then there are second and third order effects are large policy changes that aren't immediately clear such as related petty crime, homelessness, changes in education attainment, changes to medical insurance expenses and so forth. More complicated than that are social changes that everybody wants to guess at, but are really a wild card.
Portugal has had great results with drug decriminalization, primarily that demand dramatically tanked. It isn't clear similar results will be achieved in the US due to cultural differences, but I applaud Oregon for being a test experiment that other states can learn from.
Please note that I have not stated any personal opinion for/against drug policy changes.