As for policy, it seems quite clear to me that no coercion (i.e. government funding/endorsement) can be justified to provide resources for such a study or pursuit. There are just way too many objections to be made, from the faith-based ones you mention, to questions of practicality and possibility, to a variety of salient economic objections. Though these objections may not compel you, they are far from trivial enough to be dismissed outright when dealing with monopolies of force and public policy. Nor does it seem that any prohibition can be justified, or even clearly defined on such a hypothetical question, for many of the reasons that you point out.

From there if we progress to a question of personal practice, this whole exercise falls apart, under the weight of too many hypotheticals, and could easily be relegated to the waste bin labeled “mental masturbation.” There are clearly many practices and supplements in use today designed to lengthen, or strengthen our lives, and each must be taken on its own merits. Clearly there have been many positive advances (eye glasses perhaps top the list,) but it is unquestionable that there have been just as many if not more, of a dubious nature (lead paint and asbestos seemed great at first.) For the most part, I would submit that every advantage that technology grants us also robs from us a small part of what connects us with the natural world (automobiles and processed foods have made us obese and increasingly disconnected from the natural environment, computers and telephones often disconnect us from real physical human contact and have decimated the American neighborhood,) and I would stress that due diligence should be paid to understand this give and take before we make a choice that is irreversible.

Even if we only look at the actual practices employed today, it can clearly be understood that life extension is not near as easy as some might suggest. The recent extensions have not only created economic and familial strains, but also given rise to a whole new slough of physiological strains, perhaps most notably in regards to neurology. All this being said, it seems incredibly hard to argue against a hypothetical externality-free life extender (without resorting to faith-based arguments,) but then it seems harder to argue that such a creation could be achieved (without resorting to science fantasy.)