This English translation is wrong. It should be “If God did not exist, we and should have to invent it.” and the two “would and “should” applied to the obligation modal construction “have to” to cover the full meaning of “faudrait.” This impersonal “falloir” verb is the strongest possible expression of obligation in the whole world, I would say. It is something that is as inescapable as the rain or the snow. It is a natural scourge.