I agree who.
It's also a very useful self sanity-check.
To examine the validity of a proposition (someone else's, or one's own), see if it applies at the extremes.
It's not a fool-proof verification of validity. But it's a practical test of a proposition. It's a tool. Not every tool is ideal for every task. But just because a screwdriver isn't an ideal hammer, it's no sensible reason to throw all your screwdrivers away.
It's a useful tool. So use it where appropriate.

And if Treb has a sensible reason for believing I have used it inappropriately, I welcome his insight on the error of my ways.

"when the bigots of this world have been privileged for as long as they have, to them equality feels like discrimination." shiftless2