Unfortunately there are a lot of people who wouldn't drive to a seedy neighborhood and risk arrest to secure drugs, but who would take drugs if buying them were cheap and safe. Some number of those people will end up hooked, and some number of those people will be breaking into houses (or worse) looking for stuff to sell so they can get their next hit.
Like I said, I don't think the putting a stop to that is worth what we're paying in terms of money and lost freedoms, but let's not pretend these substances were made illegal out of groundless malice. If and when we end the drug war there will be more junkies, more crack whores, more people who sit around staring at the wall instead of working and raising families, more people in the ERs from overdoses and drug-fueled mental breakdowns. It's a price I think we should pay, but it still a price.