They go hand in hand. In most professions you need to be about 40 to be competent. When you're young this doesn't seem likely because you don't see many competent middle aged people: that's because they're up in management actually running things. Unfortunately we start aging mentally around the same age, and at 60 we're not really capable of creative work anymore.

So we live 80 year lives, but with only about quarter of that really giving all we're capable of, and a fair share is being dedicated to raising children. Living an extra 20 years isn't a perk - it literally doubles our most productive years. Living an extra 40 years with most forms of dementia fixed? That's almost unimaginably more productive, and unimaginably richer. Both on an individual level (working+learning more = earning more), but as a society.

You mentioned "when it's more worth living". Not sure what context you're coming from, but life is a lot more worth living in its second half, simply because you know more about how to live it, and have the means to do it. The only problem is you're getting old and senile.

Edit: please don't downvote somebody asking questions.

Suppose, right now, normal life expectancy was 200 years. How would you feel about a new program being rolled out to impose disease and death on everyone over 80?

This seems fallacious to me, the scenario you describe has zero opportunity cost for being alive till 200, it's free. Assuming no afterlife, you gain nothing by artificially limiting your lifespan to less than half its amount.

But in reality, there's opportunity cost to trying to extend your lifespan, it's all the money and attention and other resources that could have gone to improving other much more certain-rewards problems.

In other words, your thought experiment is a fully general purpose argument for any investment. It's conclusion is that you should _always_ go for the investment no matter what the opportunity costs.

Example (1) - We should expand the data center from 80 servers to 200 servers

= Why? our loads are not high, we should instead focus on improving the product

- Well imagine if we already had 200 servers in the data center, would you scale it down to 80

Example (2) - We should invest in renewable energy

= Why? nuclear power is much more certain and mature

- Well imagine if we already had renewables, would you phase it out in favor of nuclear?

In both cases, you're completely missing the point of your opponent by the "Imagine if we already had" maneuver, we don't, that's why your opponent is against it, it's a risky investment with uncertain rewards and plenty of same-utility alternatives (in the opponent's view).

If opportunity cost means anything at all, “not extending one’s life” must have a truly dizzying opportunity cost.

Good argument, in the spirit of the reversal test https://en.m.wikipedia.org/wiki/Reversal_test

> Alfred Nordmann argues that the reversal test merely erects a straw-man argument in favour of enhancement.

Yes, basically as a fellow commenter argues. Thank you for the link.

16 billion people stacked on earth?It's a pointless hypothetical because violence would have prevented that scenario long before. And what grand violence it would be! So much easier sending great-great-grandsons into battle than sons and grandsons.

It seems much easier and more feasible than inventing an FTL space drive. If you could live to be 10,000 or 100,000 years or more you could visit interesting places.

It can, and should, be both.