Yesterday I mentioned the gemara (Sota 12) quoted by Rashi that Amram divorced Yocheved because he did not want to have any more offspring given Pharoah's gezeira to kill all male babies. When Klal Yisrael saw what Amram did, they followed suit.
Everyone is learning daf yomi these days, so Brachos 10 is inyana d'yoma: Chizkiyahu was on the verge of death and so Hashem sent the navi Yishayahu to go visit him and tell him that he is being punished for not fulfilling the mitzvah of having children (Since when is a bitul aseh a reason to be chavay misa? Sorry, not my topic for now.) Chizkiyahu argued that he cannot be blamed -- how can he have children when he knows that from him will come the wicked king Menashe? Better to not have children then to bring such evil into the world! Yishashayu, however, rejected that reasoning. "B'hadei kavshei Rachamana lamah lach?" Your job, Chizkiyahu, is to fulfill Hashem's command, not to make calculations and cheshbonos as to whether that will end up being a good thing or a bad thing. Chizkiyahu relented.
Achronim ask how to fit this gemara together with the gemara quoted by Rashi. Why should Amram have worried about how he can have children in light of the danger of Pharoah's decree? "B'hadei kavshei Rachamana lamah lach?" Our job is to just do the mitzvah, not make cheshbonos.
You don't need lomdus for this -- some basic chilukim are enough to answer the question.