This holiday, many visitors to Israel are preparing to keep 2 days of Yom Tov, in contrast to the Israelis around them. And many Israelis visiting or even living abroad are planning only one day of Yom Tov.
Here's what I don't understand. If keeping the minhag of your home country is because of minhag avoteinu b'yadenu, then the current practice makes no sense.
The reason that the Jews in Bavel (Babylonia) kept 2 days was because they didn’t know when Rosh Chodesh of that month really was, since that time was set by the sighting of the new moon in Jerusalem. Even with the signal fires, the messages wouldn’t always go through, sometimes because of natural occurrences, sometimes because of Shomronim (Samaritans) deliberately lighting false fires to confuse the dates.
Well, why didn’t they just send a messenger? Well, obviously, a messenger couldn’t make the trip on time. If he could, there would be no need for the much speedier signal fire system.
So what about a traveler who lived in Jerusalem but was spending Sukkot in Bavel? Could he travel any faster than the messenger could have? Obviously not. So to spend Sukkot in Bavel, he would have to have departed Jerusalem well before Rosh Chodesh Tishrei. So how would he have had any idea when Rosh Chodesh was declared, any better than those who lived in Bavel year round? No way at all! So he would have had to keep the same 2 days of yom tov that everyone else did there, despite of that fact that most of the time he lived in Eretz Yisrael!
Today we have a set calendar. Even if we didn’t, we have instantaneous communication with Eretz Yisrael. We could get word immediately of the time of the molad (new moon) in Jerusalem. But we commemorate the way it was done in ancient times by keeping 2 days of Yom Tov outside of Eretz Yisrael because of Minhag Avoteinu B'Yadenu.
Well, if we’re keeping it the way it was done then, what sense does it make for someone who just happens to live in Eretz Yisrael to keep one day of Yom Tov in the Diaspora? His corresponding traveling ancestor wouldn’t have been able to do so. How is it consistent in any way for him to keep one day while all around him the other Jews are keeping two?
And once we establish that, the converse must follow – a Diaspora Jew should keep only one day in Israel. Otherwise the system has no consistency.
I'm not trying to mock the minhag, I'm just genuinely trying to understand. So how is the minhag of keeping 2 days in E"Y following Minhag Avoteinu?