Not arresting someone who is doing something illegal (drugs, or anything else) then sets a precedence that it's ok to engage in that behaviour. So while not arresting that one particular person might be beneficial to them, it doesn't benefit society as a whole and may end up normalising undesirable behaviour.
But there is no benefit to society by incarcerating someone removing the possibilities of a functioning life. Does Louisiana benefit by having 1 out of 7 black men either in jail, or on parole? The private prison system, sure. But does Louisiana overall? Not a chance.
We could arrest them but not send them into prison. Drug use should be a misdemeanour offence that simply forces you into increasingly more intensive therapy, rather than going with the 'therapy' of jailtime and cold-turkey.
