000646,
Anyone has the right to argue on Rav Moshe on halacha, but it is rather silly to do so if one hasn’t learned the entire shas, tur and shulchan oruch hundreds of times as he did. If your rabbi did, then kol hakavod! You mentioned that having a different opinion than Rav Moshe on halacha is like having a different opinion than anyone about any other topic. You are correct. A pulpit rabbi who doesn’t know shas and poskim inside out and then goes and argues on rav moshe is like a layman who once read a couple of science books walking into NASA and giving his opinion about how they should build the next space shuttle. He is free to express his opinions on the matter but nobody will take him seriously.