Problem: A plant is somehow illegal, and we spend billions of dollars making sure that people don't have this plant. It's a dumb waste of money.
Answer: Decriminalize possession and legalize mass distribution. Basically, it's not a crime to have, to grow, or to use weed, but if you want to sell weed to others for profit / as a business, you need to go through legal channels to make sure you're selling a safe, consistent product.
Original source can be found here.