If someone can easily and safely come off drugs on their own, then obviously that is exactly what they will do. For those that can't it will just be an increase in crime, and people leading a more furtive lifestyle.
If the interest is to punish people and save money on welfare, I think it may work.
If the interest is to get people off drugs and reintegrated into society I have strong doubts.
I suspect from the way you speak your interest is to punish and save money so I imagine for you it will work - unless one day you suffer a theft from one of these people needing to feed their habit and put food in their bellies.