I've seen some pretty large cannabis plants in my time, but one that yields a pound would be about four times bigger than the larger ones I've seen.
Clearly you know very little about cannabis or cannabis plants. 
Most people would be very, very lucky to get between two and four ounces off a plant. Five of those plants would be about a pound. A heavy smoker will smoke an ounce to an ounce and a half a month. Five plants at four ounces each, would be about a year's supply, but nothing would be able to go wrong, and every plant would have to produce at its optimum projection, and in nature, that just doesn't happen.
Your argument is ill informed and exaggerated, at best.