Are U.S. drug users and their addiction the reason why Mexican drug cartels enter America?

The answer is simple. As long as there is a demand, someone will always be there to supply the product. Years ago when the government outlawed alcohol it still flowed as if there were no end. Bootlegging was at a all time high. The same is true with drugs. When there is lots of money to made, someone will always step up and deliver. The only solution is to break the habit of drug usage. If there is no demand, then the drug flow will stop. There would be no money to be made if people did not want the product.