Because "good" is an indefinable notion,
Because "good" is an indefinable notion,
If there were such people, we couldn't explain to them what ethical judgments mean.
Imagine blind people with no notion of "yellow"; you couldn't explain to them what "yellow" means.
Because "good" is an indefinable notion,
We know what "good" means -- just as we know what "yellow" means. But we can't explain either term using simpler notions.