> Thinking about human life in any other terms than input and output is objectively a luxury, afforded only to societies with surplus resources

Even a little bit of anthropological study shows this is false.

Okay, so when you, BobbyJo, become too old or unwell to work; other people should just shoot you in the head and take your stuff, right? It would only be efficient. Or does this 'harsh reality" only apply to other people?

Modern society has the luxury of surplus resources at the moment, and we are able to take care of the old and weak, which we indeed choose to do. If/when that ceases to be the case, the harsh reality will apply to everyone, me included, yes.

Another thing humans are arguably good at is making a longer term plan and investment: if we see that old people simply get shot, we won't be investing surplus value into our retirement funds — at least not of the same sort. Perhaps we'll be building fortresses when younger, accumulating wealth to be able to pay soldiers to protect us etc...

Wait, that's exactly what has happened, except it has evolved into a more systemic solution (our taxes and social contributions pay for police, courts; bigger accumulated wealth allows for more options...).

It is a luxury we can, as a species, afford!

We actually have the capacity and capability to house, feed, and clothe everyone on the planet, and then some.

The frame can shift because our capabilities have increased.

I mostly agree. We have the capacity at present, but only because we are burning a ton of non renewable energy.