Rich…rav belsky was against many large scale eruvin, for different reasons. Us talmidim did not carry in Yerushalayim, for instance.
As regards to the matirim, besides rav yechezkel roth and rav menasheh klein, which over high profile poskim were provably matir it?
But even they did not request an eruv, but rather endorsed it after it was made.
They’re also not infallible, and benechilas kovod torasam, it is questionable to undermine the accepted minhag based on a psak from the gedolei hador of a generation preceding them.