Neville,
Since you do seem to be clear yourself about Rav Moshe’s shittah, let me ask you a few questions or riddles and we’ll see if you can answer them without looking them up first (we’ll take your word for that):
1) Which Volume and Siman is the teshuva about Flatbush and which about Boro Park?
2) What are the facts and statistics that Rav Moshe states and upon which he bases his prohibition?
3) What did Rav Dovid ben Rav Moshe pasken regarding West Rogers Park (I wonder if you know where that is without searching)?
4) In what respect is West Rogers Park equal or different than Brooklyn?
5) In what respect is Kew Gardens Hills equal or different than Brooklyn?
6) How can there be even the neighborhood eruvin in Lakewood today, if according to Rav Aharon (as well as Rav Moshe Weissman, Rav Bick, Rav Soloveitchik x2, and on and on) most of them are reshus harabim?
7) How can some chasidim who emigrated from Boro Park (where they don’t use the eruv) to Linden and its environs suddenly be able to establish an eruv which wouldn’t work according to all the poskim in question 6?
8) Why are people when they’re in Flatbush they wouldn’t use the eruv yet when they’re, say, in Baltimore they’re happy to use one – being that practically the only posek that would distinguish between them is Rav Moshe?
