Advocates for rapid and widespread development of engineered longevity are making some progress in dismissing the Tithonus Error - the common and mistaken belief that longevity-enhancing medicine would make a person spend more years as a frail and decrepit elder rather than more years in the prime of life. As more people come to see a future of longevity therapies as personally beneficial, however, a more insidious form of opposition will come to the fore.
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.
Death cult environmentalism of the "too many people" variety is, fundamentally, a failure of understanding. It is to look at the undeniably bad situations and unpleasant regions of the world and say "this is because too many people are using too many resources," rather than to see that in fact it's all due to misallocation of existing resources and the failure to develop new resources - a grand procession of waste, corruption, and the inhumanity with which human beings treat one another. These situations are problems that can be solved through development and tearing down corrupt systems of rulership - they are not immutable facts of life that must lead to the deaths of millions.
I've spoken of this in the past, so I won't rehash it at great length here:
What some presently view as "overpopulation" is more accurately described as crushing poverty amidst the potential for plenty and resources left unused. This is the result of despotism, corruption, economic ignorance, short-sighted greed and the inhumanity of man unto man - it is not a matter of counting heads. ... Here, then, is a short guide for kleptocrats and egalitarians who want to keep their countries poor. All of these policies have stood the test of time as techniques for creating and maintaining poverty. The list is by no means exhaustive, but it will give would-be political leaders a good idea of how to start their countries on the road to ruin.
And yet, alongside the ethos of human rights and the development of heroic medicine, contemporary society appears estranged from its own humanity. To put it bluntly: it is difficult to celebrate human life in any meaningful way when people - or at least the growth of the number of people - are regarded as the source of the world's problems. Alongside today's respect for human life there is the increasingly popular idea that there is too much human life around, and that it is killing the planet. ... today's Malthusians share all the old prejudices and in addition they harbour a powerful sense of loathing against the human species itself. Is it any surprise, then, that some of them actually celebrate non-existence? The obsession with natural limits distracts society from the far more creative search for solutions to hunger or poverty or lack of resources.
What I do want to direct your attention to, as the 4th Strategies for Engineered Negligible Senescence conference drawns near, is recent work by Leonid Gavrilov and Natalia Gavrilova on demographic models for scenarios of enhanced longevity. For all that everyone and their dog seems willing to stand up in casual conversion and predict Soylent Green the moment that greatly enhanced human life spans are mentioned, there hasn't in fact been much in the way of full-on scientific work done on predicting the demographic results of radical life extension. Over the past year or two the Methuselah Foundation, and now SENS Foundation, have been trying to remedy this state of affairs, and this work by the Gavrilovs is one of the first results of this strategy:
Analysis of already existing computer programs for population projections revealed that many of them are based on short-sighted assumptions of small incremental changes in human life span, and they do not allow making detailed projections for the oldest age groups of the population (which are often collapsed into one single 85+ year category). For this reason, many already existing computer programs of population projections are not well suited for the purpose of this project. Therefore, with the support of the Methuselah/SENS foundation, a new demographic projection software has been developed in this study, which was then validated for consistency of results with traditional approaches. This new demographic software is based on generally accepted cohort-component method of population projections. A number of different demographic projections is considered in this project, assuming several scenarios of life extension.
A general conclusion of this study is that population changes are surprisingly slow in their response to a dramatic life extension. For example, we applied the cohort-component method of population projections to 2005 Swedish population for several scenarios of life extension and a fertility schedule observed in 2005. Even for very long 50-year projection horizon, with the most radical life extension scenario (assuming no aging at all after age 50), the total population increases by 35 percent only (from 9.1 to 13.3 million). Moreover, if some members of the society reject to use new anti-aging technologies for some religious or any other reasons (inconvenience, non-compliance, fear of side effects, costs, etc.), then the total population size may even decrease over time. Thus, even in the case of the most radical life extension scenario, population growth could be relatively slow and may not necessarily lead to overpopulation.
If you're interested in more details, there's a powerpoint version of the SENS conference presentation that can be downloaded from the Gavrilovs' site.
Sadly none of this seems likely to change the minds of those folk emotionally vested in a Malthusian view of the world's ills - they already choose to reject plenty of very straightforward, easily demonstrated forms of data that refute their position. Once more study is just one more study, and removing Malthusianism from its place of great and malicious influence over the minds of billions is likely to be a long struggle.