David –
How do the other poskim you refer to understand shishim ribo?
(However, those who understood that shishim ribo applies to a city would have to explain what halchically defines a city.
Considering that New York City — of which Brooklyn is a part of — has a population in excess of 8 million, seemingly the other poskim you refer to would to have to prevent an eruv in NYC.
FWIW, Long Island, which Brooklyn is part of together with Queens Nassau and Suffolk, has a population of over 7.5 million.
Moreover, as Rav Moshe admitted there were cities that erected eruvin that contained a population greater than shishim ribo.)
And how did Rav Moshe explain why those eruvin were permitted in those cities with a population greater than shishim ribo?
Why would we exclude the summer tourists and guests? My understanding is that Rav Moshe uses the highest population day of the year.
And most importantly, even after we agree we don’t include the entire Brooklyn (since it is greater than 12×12 mil), what makes you confident that the 12×12 subset still does not exceed 3 million? Brooklyn’s counted census sometimes came to 2.75 million. Then you must add the undercount. And you must add the workers/guests/tourists. Surely that is well in excess of 3 million for Brooklyn as a whole, so even a subset may contain 3 million on its own.
And why then did Rav Dovid shlita, while allowing it in Chicago, still oppose it — even now — in Brooklyn?
And perhaps the 12×12 mil subset for Chicago has a smaller population than the 12×12 mil subset for Brooklyn.
Which metzius/facts are you asserting Rav Moshe was mistaken about? Brooklyn’s population? Brooklyn’s workers/guests/tourist count? And whatever facts it is you assert he was mistaken about, what was the correct figures and what figures did he assume? (And on what basis do you believe he assumed the figures you claim he assumed.)