Women, regardless of how ugly they're, can only date (or in this case, fuck) up. No woman, even if she has the lowest self-esteem imaginable, knows she's the ugliest girl in a 10km vicinity, will willfully have sex with a man she perceives as uglier than her. In her mind it's unimaginable to do so, it simply doesn't register to them. They will always attempt to seek someone who they know has more value than them on whatever characteristic (prettier, richer, more social status, etc, etc).
The only solution for both femcels and incels are sex robots.(ok incel)