I disagree, it's more an argument that even though advancement of human capability can bring great gains (defeating the dragon) we need to pursue equitability in these gains or otherwise they are unethically allocated.
The rising tide should raise ALL boats, otherwise inequitability will lead to social instability as seen througout human history so far.
While I agree that modern societies and especially global wealth are very inequitable I think medicine is one of the areas where it is almost universally agreed in practice to raise all boats. Generic medications are made available, foreign aid is often in the form of medicines and medical support, and global institutions are funded with the aim of raising all boats. Should life extension become possible through medicine or treatments it seems likely that the existing process of trying to achieve global medical equity will continue. Clearly life extension will be very highly valued and if it is out of reach of 95% or 99% of the human population there will be intense pressure to socialize its benefits to everyone. Where I can see problems is if life extension is out of reach of 50% or 75% of the world population due to material/equipment/personnel costs; that's a lot harder to socialize globally and would be similar to advanced cancer treatments and organ transplants/replacements which could be seen as the leading edge of longevity treatments.
I don't think there's a moral argument against expensive cancer/organ treatments being made available in wealthy countries; it doesn't seem like any progress on treating those diseases will be made at all if the treatments can't be made available, regardless of their extreme inequity.
The rising tide should raise ALL boats, otherwise inequitability will lead to social instability as seen througout human history so far.