Apparently, imprisoning someone in Canada costs over $100,000 a year. Right off the bat, that is clearly a substantial investment of resources. It gets even worse when you consider a few further aspects.
Firstly, it seems highly dubious that prisons play a rehabilitative role. Those who are incarcerated will probably deal with a lengthy stigma afterward, perhaps for the rest of their lives. This will worsen their employment prospects and reduce the welfare of their family members. It is also plausible that having a record of incarceration increases the relative appeal of crime as a means of financial subsistence. Before you have such a record, you have a lot to lose from a criminal conviction; afterward, you have fewer legitimate job opportunities and less to lose from a longer record.
Secondly, it seems clear that the government could spend that sum of many in a great many more productive ways. You could probably finance someone’s entire undergraduate degree for that amount, or provide an apprenticeship program for a trade. You could do a lot of preventative medicine, or invest a fair bit in deploying improvements in energy efficiency or renewable energy generation.
It seems particularly absurd to imprison people with a non-violent involvement in the drug trade. It is a normal characteristic of human beings to want to experience altered states of consciousness. It is one that we positively encourage in some cases, such as the thrill from athletic exertion or Hollywood movies, and tolerate and regulate in others, such as with alcohol and tobacco. It seems utterly foolish to imprison those who seek to alter their mental state in unauthorized ways, or assist other people in doing so, when that choice is costly to everyone in terms of lost opportunities, and especially costly to the person being punished, in terms of future prospects.