Do you see our ability to produce food keeping pace with the enormous surge in human population that this breakthrough would cause?
Also, this breakthrough would be another cause to develop the ability to colonize our solar system and beyond.
I don't see these positions as arguments against rejuvenation, simply things to consider. I really can't see a moral argument against rejuvenation.
I think this will just be a question of energy. As soon as there is energy abundance, enough nutrients can be produced to feed the world's population.
Lots of bugs around to eat, or just give immortality too the Non-Breeders that are productive and educated. A Cricket Chocolate Bar isn't suppose too be that bad anyway.