Over at Ouroboros, a look at the enhancement debate and how it impacts advocacy for engineered longevity:
I suspect that the structure of arguments about cognitive enhancement will mirror those of future debates regarding lifespan extension.
Both fields involve treatments that promise to improve or increase a parameter of human performance - one that varies to some extent within the natural population, but that seems fixed for a given individual. In both cases, human beings are 'fine' without the intervention - that is, we live comfortably (and, for the most part, happily) knowing that there is nothing much we can do to make ourselves smarter, and looking forward to our allotted threescore years and ten.
Beginning from the premise that what isn’t broken ought not be fixed, or that the 'natural order' of things ought not be meddled with, critics of both cognitive enhancement and lifespan extension may argue that neither sort of intervention in Normal Human Lives(tm) is warranted.
Pro-death advocates like Leon Kass have already argued extensively for forcing people to age, suffer, and die on just this sort of "natural order" argument. Which they apply selectively, of course, by not arguing that we should go back to living in caves, catching food with our teeth, and abandoning all that we have made.
To my mind, that there are any people at all who argue against future human enhancement through technology (while eagerly availing themselves of present human enhancement through technology) implies that this has much more to do with fear of change than anything else.
Some people would rather embrace any present horror than even the most positive change. This is not one of the better traits we humans seem to have hardwired in our evolutionary heritage.
A great many people grow up with what they know - having things far better than their parents, despite the efforts of past luddites who strived to block advancements - and then spend the rest of their lives fighting against visionaries who are trying to make things even better.