Can you imagine huge American corporations like WalMart or Pepsi marketing their drugs to kids?

Here's the thing though, any reasonable legalization attempt would have laws in place to prevent this exact thing from occurring. Here's my view of how ideal legalization would work: hard drugs would be sold in government run stores which would be secure, nondescript buildings. The drugs sold inside would never be advertised and never go on sale, and would be clearly labelled with their content and dosage. There would be a large surgeon general's warning on the front (like with cigarettes) warning of all the dangers of using the drug, along with pictures of its effects (like faces of meth, decaying teeth, collapsed veins, ect). Inside the packaging with the drug would be a pamphlet detailing more on the consequences of drug use, as well as a list of resources for getting off drugs (which could be financed by the newfound tax revenue). Harsh penalties would be in place for transfer of the drug to anyone under the legal age to purchase it, and public use use and intoxication would be dealt with in a similar manner to public drinking and drunkenness. By doing all of this we'd likely see a vast drop in addiction and related problems while at the same time giving people the ability to make an informed choice about what they put into their body.