I'm pretty sure neither I, nor the comment to which I was replying was referring to the knowledge (or ignorance) of the link between sex and pregnancy. At least in general.

The problem for something like contraception, which is the context here, is in understanding the details. Those details are sorely lacking in plays, songs, fairy tales, and old wives' tales.

> It also happens to be knowledge that's necessary to continue the species

No knowledge is actually necessary, as mere ignorant performance of the act is sufficient.