The demographic transformation in our society resulted from better living conditions and improved health status. Why should we promote health when long life spans only create health, economic, and social problems for us?
Just to clarify what you mean by this question: why promote health, or why promote health care? Each question is certainly valid; and it's beneficial to reflect on both. An important distinction exists between the two that should be clarified before going any further.
- Health promotion involves creating the educational, organizational, economic, and environmental supports that enables work toward a state of "optimal health". In a sense, health promotion is preventive health care.
- Health care refers to a traditional view of health---diagnosis and treatment of disease, repair of injury, prescriptions, doctors, hospitals, and so on. In order to make the distinction more clear, some people may describe our (U.S.) health care system as an "illness-care," or curative system.
In 1947, the World Health Organization (WHO) expanded their definition of health as "physical, mental, and social well-being, not merely the absence of disease." Spiritual well-being has since been added to this definition. In the 1950s, Dr. Halbert Dunn, the first director of the National Office for Health Statistics, introduced the idea of high level wellness (HLW). He defined it as "an integrated method of functioning which is oriented toward maximizing t he potential of which the individual is capable, within the environment where s/he is functioning." Dunn believed that ordinary people could learn to know themselves, and become better balanced and able to deal adequately with problems. As a result, being "healthy" is not simply the absence of disease.
You're perspective certainly makes sense as many of the advances of this past century (e.g., development of vaccines and antibiotics, environmental and sanitation changes) have improved the health status of our society, yet some would say that we've traded one set of problems for another. Today, the ten leading causes of premature death, things like diabetes, heart disease and certain cancers, are almost all preventable. We have the ability to focus on preventive health care if we choose to. We can help lower the incidence rate of many of the diseases which lead to untimely and costly deaths. We can also help people learn to accept their mortality and to decide when not to seek treatment if it means years of pain and financial burden with little hope of recovery.
Does this mean that we do away with our current health care system? There are times when diagnosis and treatment of diseases or repair of injuries are valuable and necessary. And no matter how hard some people try, everyone gets sick or develops a medical problem once in a while.
The important point to make is that a system which incorporates both a curative and preventive approach to health and wellness would be extremely effective. Promoting health could help many lead healthy, satisfying lives and translate to a population less dependent on medical treatment, less likely to develop chronic diseases or self-destructive behaviors, and more likely to become productive, generally happy members of our community.