As a fraction of people will know from reading the title, this article is meant for Bayesians, effective altruists, and the rationalist community in general. Bayesians are people who think in probabilities, and upon encountering new evidence, they intentionally update their assessments of what is likely to be true.
As our ability to affect the aging processes has been dramatically improved within the past decade, now is an excellent time for rationalists to consider new evidence regarding the necessity and feasibility of rejuvenation biotechnology.
Aging Causes Tremendous Harm
The amount of harm caused by aging is immense from a human standpoint. It is, by far, the greatest threat to living people today, even in the most violent of countries. (It has long since dethroned the previous all-time killer, infectious disease, which we did something about.) In a world with untreated aging, everyone who does not die of something else will suffer from decades of declining health. Cancer and heart disease have strong age-related components. Many people are subject to intensely painful conditions along with neurodegenerative disorders that rob them of their memories and ability to reason.
Death is the inevitable result, and the vast majority of these deaths are followed by cremation or burial rather than cryonics, the effectiveness of which has yet to be proven in human brain tissue. A human being is dying of old age every second of every day.
All of this, if left untreated, will be the fate of you, the rationalist reading this, as well as that of your friends and family.
Aging is a global tragedy from an economic standpoint as well. Aging is the largest driver of healthcare costs in the United States . As birthrates remain low and unhealthy lifespans remain relatively long, the proportion of the economy devoted to taking care of older people can only increase. This economic burden represents an enormous expenditure of human labor, as large amounts of money and time are spent on keeping people alive as their bodies slowly fail them.
Furthermore, many diseases of aging have early-onset counterparts, some of which affect people in middle age and others of which affect children. Progeria, for example, is caused by a genetic malformation of lamins ; malformed lamins also affect multiple aging processes , and interventions in this area are currently being investigated.
Aging Can Be Brought Under Medical Control
Fifteen years ago, the idea of intervening against aging through rejuvenation biotechnology was widely considered unfeasible or outside of human ability; today, it is mainstream science. The Hallmarks of Aging  is one of the most frequently cited papers in biology. A wide variety of researchers at prestigious universities are actively involved in pursuing rejuvenation biotechnology therapies. Multiple biotechnology companies are developing interventions against the Hallmarks of Aging, each one of which has at least one partial intervention currently in development.
Of course, it is not guaranteed that all of these therapies will prove to be clinically successful; however, even failures allow researchers to learn from their mistakes and offer further insight on how we can bring about the end of aging.
For any given person, it is possible that partial interventions may delay enough of the aging processes long enough for further interventions to allow for more healthy years of life, until, ultimately, a comprehensive suite of therapies is developed to control all of the aging processes. This concept is called longevity escape velocity.
Nothing Is Coming to Save Us Any Time Soon
There is a subset of rationalists who believe that artificial general intelligence (AGI) will be developed in the future. For our purposes, the question is not if this will occur but whether it will occur before computer-assisted human beings can make comprehensive, meaningful interventions against the aging processes and thereby save human lives. The development of a general intelligence is still not yet within any defined time horizon that AI experts widely agree upon. Multiple rejuvenation biotechnologies are in development now.
Even if you predict the development of a friendly AGI within a relatively short time frame, consider that the best AI researchers may be affected by neurodegenerative diseases before this occurs.
There are no currently feasible methods of solving the problem of aging other than rejuvenation biotechnology. The very best dietary and exercise practices are of limited use, and while some supplements help to clear senescent cells, they are simply not nearly enough.
Your Help Is Needed
Unfortunately, aging is an enormous problem, not just in terms of the harms it does but in the number of specific therapies that will need to be successfully developed in order to completely control it. The current amount of effort is significant but not enough to bring about the medical control of aging as soon as would otherwise be possible.
As a rationalist, you know better than to suffer from the bystander effect, waiting for someone else to do what needs doing. If you have the aptitude and are entering college, consider becoming a researcher yourself. Alternatively, you can aid advocacy efforts by becoming a Lifespan Hero, fund research efforts by donating to campaigns on Lifespan.io, or, if you are an investor, join the Longevity Investor Network in order to finance the development of rejuvenation biotechnology companies.
Even if the efforts of the entirety of the rejuvenation community bring forward the defeat of aging by only a single day, this will save the lives of a hundred thousand people, and one of them has a small chance of being yourself or someone you care about. It is more plausible that our efforts will bring things forward a month (3 million), a year (36 million), or even five years (at least 180 million human lives saved, more than half the population of the United States).
Aging is, by far, currently the greatest source of harm to human beings in the world. It is possible for medical science to make meaningful interventions against aging and allow many people living today to live a great deal longer than they would otherwise. Nothing except rejuvenation biotechnology is going to save these lives. Rejuvenation advocacy, research, and development efforts need all the help they can get in order to bring about the end of aging more quickly. Therefore, the best thing for a rationalist to do is to immediately aid in intervening against it.
 Alemayehu, B., & Warner, K. E. (2004). The lifetime distribution of health care costs. Health services research, 39(3), 627-642.
 Mounkes, L. C., & Stewart, C. L. (2004). Aging and nuclear organization: lamins and progeria. Current opinion in cell biology, 16(3), 322-327.
 Reddy, S., & Comai, L. (2012). Lamin A, farnesylation and aging. Experimental cell research, 318(1), 1-7.
 López-Otín, C., Blasco, M. A., Partridge, L., Serrano, M., & Kroemer, G. (2013). The hallmarks of aging. Cell, 153(6), 1194-1217.