This world of ours is not overpopulated. There is no overpopulation. A great many aspects and consequences of human society and human nature are wrong, unpleasant, and downright malign - but a lack of resources or space is not on that list. Where there is suffering, hunger, and inhumanity to others, you will inevitably find it taking place amidst the squandered potential for plenty: resources left untapped; poverty run rampant thanks to political kleptocracies; meaningless war and destruction instead of trade to benefit all sides.
But the iconic Malthusian looks at the mess made of some parts of the world and doesn't see mismanagement. Instead he sees nothing more than too many people - which means that his proposed "solutions" are varying degrees of useless, counterproductive, and outright evil. Unfortunately, iconic Malthusians are everywhere. Malthusian thinking suffuses modern environmentalism. An entire generation of Western civilization is taught overpopulation as an uncritical fact.
By far and away the most common reason I see given these days in opposition to engineered longevity is fear of overpopulation. Environmentalism has become almost a religion in its own right now, and many strands of that religion are essentially death cults: loose networks of like-thinking people who fervently believe, for whatever reasons, that the world is dying, that humans already live too long, and that people should be forced to relinquish technology and return to a simpler era. Extreme fringe variants of the environmentalist death cult really do stand for the complete destruction of humanity, but even supposedly reasonable, middle of the road people are influenced by deathist environmentalism to the point at which it is seen as reasonable to say that (a) too many people exist, and therefore (b) the unending horror, pain, and suffering of death by aging is necessary.
A sterling article at Spiked Online hits all the right points:
In the year 200 AD, there were approximately 180 million human beings on the planet Earth. And at that time a Christian philosopher called Tertullian argued: 'We are burdensome to the world, the resources are scarcely adequate for us… already nature does not sustain us.' In other words, there were too many people for the planet to cope with and we were bleeding Mother Nature dry.
In the early 1800s, there were approximately 980 million human beings on the planet Earth. One of them was the population scaremonger Thomas Malthus, who argued that if too many more people were born then 'premature death would visit mankind' - there would be food shortages, 'epidemics, pestilence and plagues', which would ‘sweep off tens of thousands [of people]’.
In 1971 there were approximately 3.6billion human beings on the planet Earth. And at that time Paul Ehrlich, a patron of the Optimum Population Trust and author of a book called The Population Bomb ... He said India couldn’t possibly feed all its people and would experience some kind of collapse around 1980.
What this potted history of population scaremongering ought to demonstrate is this: Malthusians are always wrong about everything.
Malthusianism is, in essence, yet another facet of some peoples' inability to see change in the world around them. Some folk see only what is, refusing to acknowledge what will be. Which is a strange state to be in given the rampant pace of technological advancement at present. New and better resources to meet any level of demand will be developed, and thanks to the operation of markets, entrepreneurs, and competition, will be developed well in advance of need. That is what we humans excel at accomplishing. More people in the world means more demand for resources, more rewards for those who find new and better ways to satisfy those demands, more opportunity for development, more minds working on science and technology, more new and improved resources developed to replace old ones.
This is the way the world has always worked, all through those centuries of Malthusian cries that the sky is falling. The Malthusians have always been absolutely, completely wrong. This is the way the world works now - and the living Malthusians are just as wrong as all their ideological ancestors.