Technically, was it a sin for Lot's daughters? No, because they
thought what they were doing was to repopulate the earth and not
for the pleasure, and as Origen said, it was a one off incident and
not meant to repeat again such that it becomes a consistent vice.
Is it a sin now? Definitely! Because GOD has specifically
disallowed it in Leviticus.
My friend, 24/7, think harder. =)
I pose the following questions to you:
1. Imagine you are the daughter. You think only three of you
left in the world .. or is it? If truly you have such virtuous
motives [to repopulate the world], why don't you *openly* ask for
Lot's cooperation?
2. The fact you have to take Lot by surprise means you already
know Lot is reluctant to cooperate with you. And why should he, if
it is a noble task after all? Does it mean Lot is committed to some
kind of incest commandment, issued long before Moses? *hint
hint*
3. On the other hand, what makes you think you are the only
three left in the world? If you know the righteousness of your
relative Abraham, is it not possible God could have saved him and
Sarah as well?
Of course lah, Lot 也不是什么好东西. He started to turn bad after
parting from the righteous Abraham and moved to Sodom. Kaoz, of all
places, he chose Sodom. Granted, he is still good or else the
angels won't save him. However Lot is not that holy after all and
as the Jewish commentator Rashi pointed out, "Lot knew what had
happened the first night with his first daughter and did nothing to
avoid the situation with the second daughter."
Cheers.