From a biblical perspective*, the intrinsic value of humans infinitely outweighs their instrumental value. With that in mind, we can say all humans are equally valuable.

If we differentiate usefulness from value, I’d say you can use the campsite litmus test. A “good” camper always leaves his campsite cleaner than he found it. A useful person therefore offers more than they consume.

The problem is that this is both subjective and brings in to play the double coincidence of wants. How do we tally someone’s total life consumption versus their total life output when so much of one’s life output doesn’t have a fair market value? My kids produce ostensibly nothing practical, yet I would sell my whole net worth AND life for theirs. So they arguably produce that much value if you look at the market rate.

Sadly, I think this impossible system is the predominate means of attempting to judge people in both a fiat and sound money mindset.

So I would defer to God, who I think has revealed himself in the bible, where people are viewed as having intrinsic value derived solely from God* (yes, by fiat! but not the fiat of man), and a very subjective usefulness.

*James 2 Philippians 2 Ephesians 1 Genesis 1 Matthew 18 Matthew 6 Etc…