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?
Perhaps I confused the issue by introducing the word "uncertainty." I'm happy to drop that word.
You started out by saying "The reason why perhaps not push the button: unforeseeable (?) unintended consequences." My point is that there are unforeseen unintended consequences both to pushing and not-pushing the button, and therefore the existence of those consequences is not a reason to do either.
You are now arguing, instead, that the reason to not-push the button is that the expected consequences of pushing it are poor. You don't actually say that they are worse than the expected consequences of not-pushing it are better, but if you believe that as well, then (as I said above) that's an excellent reason to not-push the button.
It's just a different reason than you started out citing.