Even a largely unenforceable law is good, because Law Teaches: and let's teach our fellow citizens that to kill a human being because of their disability, is murder. Every time we make them admit "Yeah, we kill Downs kids for the precise reason that we want them dead," their mask slips another couple milimeters.
Expose them for what they are. If nothing else, expose them to themsleves.
They already have exceptions based on the reason of gestation time.