Pro: An extended lifespan would enable an individual to contribute more to society than would be possible in only the average lifetime.
Pro: Each generation must go through a difficult and time-consuming period of education. We need to learn lessons from previous generations. This wastes time and energy.
Con: If many people live longer than normal lifespans, they would place great burdens on society. If reproduction is not kept under control, if births continue indefinitely to outnumber deaths, then severe strains on systems for producing and distributing scarce necessities will inevitably occur.
Con: Death brings renewal to the social and political realm: It breaks the stranglehold some people have on political institutions and shifts power to those with new ideas. Moreover, those who would have a chance to achieve a greatly extended lifespan would likely become very cautious and conservative; they might even become obsessed with their own safety. Society would stagnate without risktakers.
Reply: Life extension would enable some of those who hold power to maintain their influence but this could be for good or evil. Death does not distinguish people with good ideas from those with bad. It does not distinguish the sensible from the foolish, the great from the mediocre. So the mortality of human beings does not guarantee social or political progress, and life extension does not threaten to end progress. Those who want to make progress or correct injustices in a society where long-lived people retain power have war as an option. Humans can always bring death back into a world from which technology has taken it.
Con: The desire for physical immortality is selfish. Life extension benefits the individual at the expense of the species. Death makes evolutionary progress possible.
Con: The weakening of the body, the loss of physical and intellectual powers, the slackening of sexual desire, the accumulation of health problems, the increased difficulties in seeing and hearing—all of these dull our enthusiasm for living. And humans become impatient when their lives become banal. If they see no prospect for improvement, if boring or painful events are repeated decade after decade, death can become desirable.
Con: Without an ability to perform miracles, that is, to conquer all diseases, to neutralize all opposition, to defeat all enemies, to render all arms impotent, no one could achieve physical immortality. Unless most other people cooperate to reduce the hazards to life, the lifespan of an individual will never be significantly extended. And yet even if a person had the full support of an entire society and even if that person had the ability to perform the miracles mentioned here, achieving an unlimited lifespan would need a miracle that no one could perform: the prevention of all accidents. That, by the nature of the world, can never be done.
The extension of the human lifespan would not eliminate the possibility of war. Those who are more willing than others to risk injury and death have an advantage over those who are more concerned for their own survival. The social and technological apparatus that extends the lifespan would fall to those who have less regard for their own longevity or to those who care little about the longevity of others.
Were the technologies that enable life extension expensive or for any other reason not easily available to many people, those who desire them may be willing to use all their resources and even risk their lives to access them. Then the desire for the means of life extension could prompt the violent actions that make extending the lifespan difficult if not impossible.