I've thought about this one, and I think drug prohibition is an unfair comparison. Drugs bring a immediate and addictive reward, that the user seeks continuously. This drives up their demand. Not to mention they have higher profit margins, and are a temporary good. If gun's were illegal, owning one would be a constant threat to the owner. Drugs can be easily disposed, and are not permanent. Decent guns are made by manufacturer's, which is much easier to regulate than drugs which are made in labs and farms. Finally, gun's are metal and therefore much harder to smuggle... metal detectors and such.

Not saying I can prove any of this, but I think the comparison just doesn't work.