If people could live for much longer then they’re likely disincentivised to procreate due to worries of overpopulation and then, in one way of thinking, you’re hypothetically depriving a line of offspring of lifetimes they’d otherwise have if you’d had what we consider a normal lifespan now.

Yes I realise there are probably an infinite number of takes on this, I’m just pointing out one possible way of looking at it for the sake of saying not all technological advances have universally positive outcomes.