Neville Chaim Berlin,
“Highly recommend you read an article published by the OU called “Major Cities and Their Eruv Status.” Eruvin in highly populated cities is not a “general concept” where if you accept one you accept them all. Each one seems to have a unique heter for its situation, and all the cities listed have more than 600K people.”
This is probably Rav Belsky’s argument, but in fact most poskim would disagree.
“Sadly, they don’t say why Reb Moshe was ok with considering KGH its own reshus separate from the rest of Queens. They do mention that he forbade the inclusion of the highways, which means the new connector between KGH and Forest Hills does not have the backing of Reb Moshe. The author of the OU piece agrees with you that this would allow for eruvin in sub-sections of Chicago.”
If one can make a subsection of Queens then one can make in a subsection of Brooklyn.
“There are plenty of extremely meikel shittos on the books, but the new Brooklyn eruv needs to detail which one(s) they are utilizing, otherwise no frum yid should be using it and signing on to blindly trust a mystery heter. Again, not talking about the BP or Flatbush eruvin, talking about the new one that goes all the way around Brooklyn.”
The Brooklyn Eruv is relying on mechitzos. With mechitzos there is no issue according to all, besides for Rav Aharon.