@sechel83 Most Gedolei Yisroel held of the Lubavitcher Rebbe ZTL as a Gadol, even when the harshly criticized many of his actions. Rav Shach was at one point a near unapposed Manhig without equal and his opinions were reflections of what most Rabbonim felt. Namely (like Rav Moshe states in the letter you posted) that Rav Schneerson ZT”L was a Gadol whose kiruv program is unparalleled, a massive percentage of his Chassidim acted in ways contrary to Yiddishkeit and he failed in curbing them.
@Lostspark I do think it’s tipshus and bordeline Avodah Zara to take a very unique neis mentioned in the Gemara and say that it can apply to any arbitrary individual or situation.
Neither of you have taken up my challenge: Go find a RANDOM selection of non-Chabad Rabbonim and ask them if it’s OK to believe that a dead man is Moshiach. If you want, you can even start with Rav Breitowitz SHLITA. Go to any Yeshivas or shul website, they almost have contact information. Just send them an email!