In most cases legal things are cheaper than illegal things.
Don't you forget about all the folks in Mexico and Central America who kill each other to keep the drugs coming with the guns they bough from Americans?
I have a friend from El Salvador who told me the whole issue would be over now if drugs had been poisoned years ago: "All the American drug addicts would be dead by now", he said. Is a good business for us, we get the drugs (some might die) and with the money we give them they buy our guns to keep the drugs coming.