If possessing/using drugs weren't a crime, then people would have less to say "I'm already breaking the law, fuck it"
You'd knock out most organized crime cause you cut their money from them.
If the city was willing to sell at cost (seriously, morphine and oxy isn't expensive to make at all), it would also destroy that economy, and potentially free some back in the hands of the people.
And at the bottom, it also looks to me is poverty and suffering, and people using drugs to buy a short while not thinking about it.