There are already 6.5 billion people wandering around as you read this. Overpopulation is a severe problem in parts of the world (India, Bangladesh, the Upper East Side).
Some time ago writer P. J. O'Rourke pointed out that the net population density of Bangladesh is no more than that of Hayward, CA. Large numbers of people die each year in monsoon-related events in Bangladesh but that is because of the country's extremely low elevation -- its highest point is 660 feet above sea level -- not because of supposed overpopulation. If Bangladesh is overcrowded, then large sections of central and southern California need to be declared national disaster zones. Ditto Manhattan, while you're at it.