Reading about the dare to say chaotic nature of Drow Noble births I am left somewhat confused. The fluff on Drow Nobility states that one out of every twenty Drow births spawns a Drow Noble. Is this statistic for female Drow Noble or a common female Drow? If the Drow still have the normal Elven conception rate it seems like noble blood lines would be at risk if so many heirs are killed at birth.
Well, on the other hand, given that Drow tend to indulge in all the 'evil' aspects of Chaos, their birth-rate would actually be abnormally high for Elves. Also, don't forget their association with the inherent underground 'magical radiation' may have induced more internal changes than just their physical appearance and inherent magical abilities. Frequent births could be the norm for Drow, along with an abnormally fast (again, for Elves) gestation cycle in which the child could be carried for 10-12 months, rather than the usual year and a half for most Elves.
Also, consider for the PCs, they find a chamber sealed and guarded heavily by magical constructs deep within the heart of a Drow City. Inside, they find all manner of Elves, Surface and Drow alike, all female and chained to the walls in demeaning ways. After freeing the captives, they learn the Drow keep their numbers high with a brutal breeding program, preventing the degeneration of Incest due to a small population by capturing surface elves and breeding them till they die due to exhaustion, fatigue or just pure soul-destroying despair, and then breeding to the half-breed children... in this way, the Drow not only increase their numbers, but destroy the future of their rivals.
If that doesn't end any conflict the more nobler PCs might have against striking down 'women' (female Drow NPCs), nothing will. Elves have moved from the Forgotten Realms Drizzt and his hellspawned armies of fanbois. They're evil because they enjoy it, they're chaotic because they flit from one brutal regiment of terror and perversion to another the way a Human changes their underwear. There is no salvation, no redemption, no hope for common ground or a live-and-let-live accord. Dwarves will walk arm-in-arm with Orcs down the streets of Chelax as brothers-in-arms before the Drow of Golarion show even a hint of remorse for their actions.
And you know what? I LIKE them like that.