@commonseychel,
The letter has a sponsor. (In fact every letter that gets Gedolim’s signatures has a sponsor.) The sponsor is the driving force behind the actual letter and is responsible for getting the signatures.
Rabbi Moshe Margareten shlit”a was the driving force behind the letter.
He loves doing good things for klal yisrael and he felt that the letter was a good thing and succeeded. He deserves tremendous credit for it.
But I am not sure that this defines a shita of the Gedolim.