This is an interesting experiment: find any random person you know and ask them what the downside would be to using better medicine to live for 150 years. Nine times out of ten, I'll wager, your friend will tell you that living for so long would be terrible because a person would spend most of his or her life decrepit, increasingly crippled by age-related conditions. In otherwords, your random friend thinks that "healthy life extension" means "being aged for longer."
This preconception about the way in which healthy life extension works is known as the Tithonus Error. It is widespread to the point of ubiquity, unfortunately. Most people dismiss healthy life extension out of hand precisely because they see no attraction in being - as they assume - increasingly aged and debilitated.
The Tithonus Error gains its name from ancient myth. As Chris Lawson writes:
In Greek mythology, Tithonus was a handsome mortal who fell in love with Eos, the goddess of the dawn. Eos realised that her beloved Tithonus was destined to age and die. She begged Zeus to grant her lover immortal life.
Zeus was a jealous god, prone to acts of deception in order to seduce beautiful gods and mortals, and he was not pleased with Eos's infatuation with a rival. In a classic Devil's Bargain, he granted Eos's wish -- literally. He made Tithonus immortal, but did not grant him eternal youth.
As Tithonus aged, he became increasingly debilitated and demented, eventually driving Eos to distraction with his constant babbling.
In despair, she turned Tithonus into a grasshopper. In Greek mythology, the grasshopper is immortal. (In a close cultural parallel, the Chinese believed that locusts live forever.) This myth also explains why grasshoppers chirrup ceaselessly, like demented old men.
As Chris goes on to explain in an article well worth reading, modern medicine will never lead to a world of "debilitated, demented" aged people. Healthy life extension means extending the healthy part of your life span, not more years of infirmity. Fighting the Tithonus Error was why I coined the phrase "healthy life extension" and go to such pains to use it everywhere rather than the more commonly used "life extension." (I'm sure I'm not the first to do this. The term "health span" is also widely used, for many of the same reasons).
In order to widen the appeal of healthy life extension and gain widespread support for serious anti-aging research, we must overcome barriers imposed by misconceptions like the Tithonus Error. This is one reason why education, of both the media and the public, is so important to the future of health and longevity.