We found this problem very quickly with legal opioid manufacturers - in the 90s, we had very lax rules on prescription painkillers, and the results were predictable. These companies bribed doctors into prescribing them to as many people as possible, lobbying resulted in a refusal to look at the problem, and now we face the fact that these pharmaceutical companies are effectively legal drug dealers to a large portion of the population. Same thing with overprescribing amphetamines to kids for ADHD.
Predictably, we've clamped down harshly on these drugs, and now addicts are turning to heroin because it's cheaper and easier to get. It's just a massive clusterfuck, and it's all due to the fact that slick-talking marketers basically said, "No, don't worry - it's just medicine. No one's going to get addicted from this. Here's a fantastic vacation package while you think it over!"
Addicts make good customers. They'll pay whatever you want, and they'll be with you for life as long as you make the product easily available to them. There's just way too much money at stake to keep companies from acting in a predatory manner, which is why we ended up with Joe Camel and other ads aimed at kids.
I don't like bringing up the "Won't someone please think of the children" argument because it's usually fallacious, but the fact is that tobacco companies have known for a long time that children are very susceptible to advertising and very likely to sustain long-term addiction if they're hooked early. I'm sure that the same is true for harder drugs than nicotine.
The only real question is "Is that state of affairs preferable to the current serious problems of the War On Drugs?" I think that there should be a middle ground. Decriminalize possession totally, go after dealers. This avoids the typical junkies getting busted and sent to long prison terms for having a dime bag, but it prevents regular business from hooking people by the millions.
All I can say is that if we totally legalize drugs, I'm investing heavily in whoever's marketing heroin. One cubic centimeter cures ten gloomy sentiments and all that.