For one thing, there is a huge difference between casual user and abuser. Everyone needs to understand that. Do I think the occasional pot user should be jailed? in my opinion, no.
I’ll leave this open for a bit longer as I normally don’t close a thread with me having the last word. However, this could be argued ad nauseam:
Do legal drugs reduce the number of dangerous or non-functional addicts, or the number of overdoses?
Do legal drugs help keep potential abusers/addicts integrated with society?
Do legal drugs reduce violence in society?
Do legal drugs offer anything for society to profit from, given the track record of abusers not showing up for work, going on welfare, and placing a strain on emergency services?