Health: I looked up what R’ Moshe wrote about an eruv in Manhattan. He originally wrote that he held it wasn’t good. However, he wrote that yesh al mi lismoch, and he would not be against those who used it, because they did have a valid opinion to go by. He even wrote that this is a machlokes in halachah and Hashem is rejoicing over it!
Later, R’ Aharon Kotler wanted to sign strongly against it, and asked R’ Moshe to join in signing a letter. Out of respect for R’ Aharon, he signed. He write a letter saying that while he initially wrote a different opinion, he signed that letter for R’ Aharon.
So to the claim that nobody can argue on R’ Moshe, even R’ Moshe himself said that he understood the opinion that the eruv was good even though he didn’t agree, and felt there was nothing wrong with relying on those opinions.