Saying that all civilizations able to create strong AI will reliably be wise enough to avoid creating strong AI seems like a really strong statement, without any particular reason to be true. By analogy, if you replace civilizations by individual research teams, would it be safe to rely on each team capable of creating uFAI to realize the dangers of doing so and therefore refraining from doing so, so that we can safely take a much longer time to figure out FAI? Even if it were the case that most teams capable of creating uFAI hold back like this, one single rogue team may be enough to destroy the world, and it just seems really likely that there will be some not-so-wise people in any large enough group.