People don't get upset when they've treated others poorly. They get upset when they're treated poorly. So the comment comes to the wrong conclusion. People deny lookism for the same reason they deny IQ. It sticks them in a box they have limited ability to get out of and forever puts any hope of being treated with primacy to bed.
The biological advantage of wanting Stacy is that you work on yourselves enough to end up with B Brenda. Aiming for the highest high still moves you in that direction. It's hard to work to be mediocre or above average, or to really understand what that entails. A lot of people on this forum go 'well I can't be Chad' and so they throw their hands up in despair and give up because to understand potential you have to understand where you are, what your failings are, what your potential is in those failings, as an agglomerate what it would mean to improve your status at to your potential, how much time that will take, how much effort that will take. Instead it's a lot easier for the normies brain stem to whisper to them 'you could be chad if you tried' and to move towards it.