[mminer237]

If I offered to pay £10 for each fresh human finger brought to me, what moral system would say the right thing to do is cut off as many fingers as possible‽ Would you sell your own fingers for £10 each? I think it's very fair to say that any person ever would value their own fingers more than £10.

[crazygringo]

Exactly. This is just "revealed preferences" that can be ordered.

Lots of things in philosophy might have debatable rigor, but this in particular isn't one of them.