We humans are capable of the most mundane of evils. Perhaps the most pervasive in this age in which no decision is permitted to be private and individual any more, in which government is used as a lever to open up access to the minutiae of everyone's lives and pour them onto the public stage to be regulated and inspected, is the evil of seeking to deprive others of a benefit that the seeker would readily make use of were it theirs. Money, and all the trappings of wealth, are the classic example. There is no evil as boring and ubiquitous as the person who works to tear down those who have more than he does, even as he strives to accumulate more for himself.
When it comes to enhancing human longevity, there is no harm done to the world by the personal choice to stand to one side, not participate, and age and die. It seems a waste and a shame, but freedom comes with the option to shun potential and refuse opportunity: it wouldn't be freedom if it didn't. All too many people who declare their intent to do this are clearly availing themselves of all the advantages of modern medicine, however. Their position is incoherent. Put them fifty years in the past and they would be arguing against the very technologies that are keeping them alive in good health. Put them fifty years into the future and they would be taking advantage of rejuvenation treatments just like the majority of the population. But again, it is a choice to act and think this way, and for so long as it is a personal choice it doesn't harm progress.
The real problem is those who seek to forge the world to their view: who would use the state as a lever to block and hold back work on rejuvenation treatments for everyone. This is a great evil, the consequences of its success measured in millions of lives for each month of delay, and the ongoing suffering and pain of hundreds of millions more.
As research related to life extension has progressed and the concept has begun to register with the mass public mind, we increasingly face objections arguing not that we can't achieve it, but that we shouldn't. In-vitro fertilization, therapeutic cloning, stem-cell research, and other medical innovations of recent times have met with the same agitated yammering about going against nature. The objections to anti-aging research are just the latest incarnation of the same old mentality.
Another tack some people take is to insist that they personally would not want to extend their lives indefinitely. I doubt this - very few people, in practice, refuse an opportunity to save their own lives when death is staring them in the face - but even if they're telling the truth, it's perfectly irrelevant to the larger issue of whether research in the field should keep going. Even when radical life extension becomes a reality, anyone who seriously objects to the idea will be free to refuse whatever therapies are involved, just as adults today are free to refuse blood transfusions or other medical treatments to which they object on whatever grounds. The fact that some people and religious sects have such objections is not a basis for arguing that blood transfusion should not have been invented.
And this is the key point: the deathist moral position is an abominable one. It boils down to saying that I need to die because of your visceral discomfiture with something.
We're already quite some ways down this road. During the [19th and 20th centuries], life expectancy at birth in developed countries roughly doubled, from about 40 years to about 80, due to vaccines, antibiotics, and various other innovations. All the clichéd objections that are now made to radical life extension - overpopulation, cultural stagnation due to having too many old people around, widening the gap between rich and poor countries, etc. - could just as easily have been made in 1900 against these achievements. But it would be an audacious deathist indeed who would argue today that we should not have invented vaccines, or should stop using them now.