Widely available marijuana that gets you just a little high would be pretty safe and soak up most American demand for the product. With a mediocre legal product, most people would not have enough incentive to jump into the illegal market. This would keep our citizens law-abiding, cut the illegal market off at the knees, and likely keep people from harder drugs (a big reason why marijuana is a gateway is that you're already breaking the law and know a dealer). We would save money on law enforcement and add to the economy and tax revenues.