You mean as opposed to, say, aborting 40 million in 26 years and not allowing them to even be born to find out if they were "weak and sickly" or not?
Those Spartan babies were a significant proportion of their newborn. The ones that met abuse might have as well been all of their progeny.
That’s a “civilisation” that doesn’t exist anymore, and been dead for centuries, if not eons, remember?
They must have messed up somewhere along the way.