Greetings.
How can there be a principle of creating an entire socioeconomic burden of second day yomtov as a mere custom of ancestors when we have the fixed calendar?? And how can it be that the mere custom of ancestors is doyche a d'oraisa of taking the lulav on shabbos first day?? What is the source in Chazal for this claim that a mere minhag can be doyche a d'oraisa?!
David Goldman, USA
The Gemara in Beitzah 4b writes that once the calendar was clarified, they would have negated the second day Yom Tov, and that they retained it as "Minhag Avoseinu b'Yadeinu" due to the fear of fresh decrees against the Jews causing them to revert to the previous situation where they would not have access to the exact date and would end up sinning (by eating Chametz on Pesach, -Rashi).
The Chachamim have the right to issue decrees (such as not holding the Lulav on Shabbos) to override a d'Oraisa as long as it is "Shev v'Al Ta'aseh" (passive) but not when it is "Kum va'Aseh" (active). See Yevamos, Daf 90a-b.
(See the Introduction of Sefer Yom Tov Sheni k'Hilchasah for an in-depth analysis of the benefits of Yom Tov Sheni, which clearly outweight the socioeconomic hardships which may be experienced. -YS)
B'Virchas Kol Tuv,
Eliezer Chrysler
Thank you, R. Eliezer Chrysler. We can understand that the requirement only exists in relation to an unstable society of persecution of the Jews that could make it impossible to follow the correct days of the calendar. A powerful argument could be made that in our time it does not apply to general society among goyim nowadays, whereby no concern for ascertaining the correct days of the calendar are even relevant anymore.