I might need a better title (It has now been updated), but here goes, anyway:
I've been considering this for a while now. Suppose we reach a point where we can live for centuries, maybe even millenia, then how do we balance? Even assuming we're as efficient as possible, there's a limit for how much resources we can have, meaning an artificial limit at the amount of people that could exist at any given moment even if we explore what we can of the galaxy and use any avaliable resource. There would have to be roughly the same rate of births and deaths in a stable population.
How would this be achieved? Somehow limiting lifespan, or children, assuming it's available to a majority? Or would this lead to a genespliced, technologically augmented and essentially immortal elite that the poor, unaugmented ones would have no chance of measuring up to? I'm sorry if this has already been considered, I'm very uneducated on the topic. If it has, could someone maybe link an analysis of the topic of lifespans and the like?
To me, the real turning point is if and when we learn how to precisely control our personalities - in short, reengineering human nature itself. Of course there's the nature vs nurture matter in this, not to mention all the potential factors than even go into a personality, let alone alter it. But I'm 100% against uncontrolled transhumanism, or even mere unregulated genetic modification or augmentation.
Though, let's suppose there was a way to correct obviously harmful behaviorial defects with at least a partial genetic basis, particularly behavior every society would see as egregiously harmful, and especially criminal (supposedly anti-social personality disorder- such as psychopathy - is one of these). Would the prospect of even reducing that behavior be worth it?
The dissonance is between the modifications you would like to see and the modifications which will dominate. Even if 99.999% wants to see a kinder, gentler, less psychopathic human, if there is one a-hole in the bunch who turns up psychopathic agression and reproduction drive in such a way that the resulting creature does pretty well, his result will dominate.
I would bet that personalities that will not kill off the other creatures who are genetically dangerous to them will never, over time, be on the winning side.