Completely agree. There are always going to be people that want to try drugs, and a portion of those people are going to be successful. A portion of those people will use drugs on a semi-regular basis, a portion of those people will become addicted, and a portion of those people will commit crimes as a result of their addiction. But why attempt punish everyone that takes drugs because some percentage of them commit crimes?
Why set up the system to amortize the public cost of addiction over long periods in the form of hospital visits, lost productivity (both directly due to addiction and indirectly as a result of former criminals' difficulty rejoining the job market), public assistance, court costs, jail costs, and prison costs, rather than focus on rehab and breaking the addiction itself?
If you look at history, drugs were almost never criminalized because they posed a public health crisis - and when they arguably did (as in alcohol prohibition), criminalization created more problems than it solved. Usually the motivations had something to do with xenophobia, moral panic, or politics. Alcohol prohibition was fueled by general animosity towards immigrants (Irish) and a growing Catholic population, with a smattering of both moralism and public health concerns spearheaded by women's rights groups. Marijuana was criminalized largely due to xenophobia toward mexicans and black people. Crack carried harsher penalties than regular cocaine because black people used it. LSD was cracked down on to quell anti-war sentiment in the Vietnam era.