Survival of the fittest (of mind)?

The current US population is over 3,000,000, and sooner or later, we'll be China II (In population terms, No offense, I am chinese myself). We need to talk about population control. So, if we do not regulate alcohol, tobacco, or narcotics, wouldn't we be rid of those stupid enough to use them? Therefore, wouldn't the population decrease, and wouldn't there would be more intellectuals compared to retards (no offense)?