Earlier quoted context omitted.
Sure they are, I debated enough to recognize that. I even debated with medical professionals and scientists to this effect. They think it's "unnatural" (whatever that means). For a short while there, my post had a negative score. They don't like to engage, but they are opposed.
So suppose you can keep old people healthy, strong, mentally sharp, etc. at what point do they get out of the way? 100 years? 110? 150? You must see that at some point the population becomes unsustainable if the old never die off.
Second, of course this kind of research eventually arrives at measures that prolong (productive) life, which gives traditional people even more to scream about. We will devour the earth! Never mind falling birth rates in industrial nations which would doubtlessly be the only countries experiencing those extended lifespans.
However, my argument is more basic than that. Because, you guessed it, I'm all for longevity research as well. It's a basic ethical appeal to not waste perfectly good minds to decay and oblivion. Conjuring up economic problems that may or may not be even remotely applicable to this type of future society seems callous and short-sighted to me.