A. A careful reading of Rav Dovid’s words in the original Hebrew  [since the loose English translation could be misleading] shows that he is in fact referring to his father’s position on the 1979 eruv and not his father zt”l’s theoretical position on the current eruv. Rav Moshe based his p’sak regarding the 1979 Flatbush eruv on information that had been related to him at the time. Since the facts on the ground have been otherwise confirmed ― such as the fact that the population of Boro Park and Flatbush is less than shishim ribo and the verified presence of mechitzos encompassing Brooklyn ― one can only extrapolate from Rav Moshe’s teshuvos how he would paskin regarding an eruv today. In light of the current situation, Hagaon Harav Tuvia Goldstein zt”l Rosh Yeshiva of Emek Halacha and a Talmid/Chaver of Hagaon Harav Moshe Feinstein zt”l, has said on numerous occasions that Rav Moshe himself would allow an eruv.
As explained in The Community Eruv kuntres, Rav Moshe concurred that if Brooklyn’s population is less than 3,000,000 it’s only prohibited to establish an eruv there because of a personal gezeirah and not because it is a d’Oraysa. [It’s important to note, Rav Dovid maintained that his father zt”l would allow an eruv if the population of a city is less than 3,000,000; therefore, according to Rav Dovid the issue in Flatbush is definitely no longer a matter of a d’Oraysa.] Consequently, when Rav Dovid stated in his letter that he heard from his father zt”l that since, “there are over 2.5 million people living in Flatbush and its environs … it is impossible to build this Eruv,” Rav Dovid must be alluding to his father zt”l’s gezeirah and not that his father maintained that the matter is a d’Oraysa. [Additionally, it’s not clear what Rav Dovid intended with this statement that “there are over 2.5 million people living in Flatbush and its environs.” According to his father zt”l, the boundaries of a city aren’t measured as one unit but rather in blocks of twelve mil by twelve mil. Since Brooklyn encompasses an area of a little more than twelve mil by twelve mil, the entire population of Brooklyn would not be included in the calculation to evaluate if it’s a reshus harabbim. Furthermore, the latest census figures indicate that the population of the entire Brooklyn is less than 2.5 million.]
It’s important to note, Rav Dovid in his letter is taking issue with only one of the three independent reasons to allow an eruv in Brooklyn according to his father zt”l.
Q. But aren’t there some other halachic reasons, besides for reshus harabim, not to allow an eruv in Flatbush.
A. According to Hagaon Harav Moshe Feinstein zt”l there is no other halachic reason [such as sechiras reshus ] not to allow an eruv. All these other claims are just proof that the anti-eruv forces are selectively choosing from unrelated shitos yachidos with an objective to asser eruvin even without valid reasons. Many people do not know much about hilchos eruvin, and they unfortunately approach the subject with a closed mind. Thus when a permissible eruv is constructed, they are quick to issue a blanket statement and declare that Rav Moshe would not have approved of the eruv in any form. In truth, Rav Moshe maintained otherwise, and he is often misquoted or misinterpreted in an attempt to validate misconceptions about eruvin. [For example, some have claimed in the name of Rav Moshe that pirtzos esser is me’d’Oraysa. Some go to such lengths to prohibit eruvin that they state things in Rav Moshe’s name that were never mentioned in any teshuvah. For example, in a speech given a while ago about the eruv in Flatbush, there was a claim made that the reason Rav Moshe allowed an eruv in Kew Gardens Hills, Queens was that the area is encircled with mechitzos. This is a fabrication, as Rav Moshe never refers to mechitzos in any teshuvah concerning Kew Gardens Hills. Nor does anyone else mention mechitzos regarding Kew Gardens Hills. More so, since Brooklyn is encircled with mechitzos as well, why should it be any different than Kew Gardens Hills? If Brooklyn would require delasos at it’s pirtzos, Kew Gardens Hills would require delasos as well. See The Community Eruv, page 37 for Rav Moshe’s real reason to allow an eruv in Kew Garden Hills.] Shouldn’t hilchos eruvin and Rav Moshe’s teshuvos be studied before an opinion is rendered? Shouldn’t the goal be to seek the truth instead of collecting all sorts of objections from disparate sources? Why must the objective always be to forbid eruvin?
 English section, page 6 and Hebrew section, page 7.
 The anti-eruv brochure, Hebrew section, page 7.
 Questions and Answers Regarding the Flatbush Eruv, page 7.
 Igros Moshe, O.C. 4:87-88, 5:28-29.
 Pages 34-5.
 Igros Moshe, O.C. 5:29; see also 4:88.
 West Rogers Park Eruv, 1993 page 23.
 Igros Moshe, O.C. 4:87-88.
 Census 2000 Summary File 1.
 See The Community Eruv, section two.
 See The Community Eruv, page 12.
 See The Community Eruv, page 42.
 Igros Moshe, O.C. 4:86 and Addendum to O.C. 4:89.
 See Minchas Chein, siman 24 and Minchas Asher, 1:51-52, 2:56-57, 2:59.
 Igros Moshe, O.C. 1:139:3.