So thegra walks in to NASA and says “There’s life on other planets, I went to one and it was inhabited by pink elephants with four trunks, six legs and thirty-nine brains who have built a civilization based on roller-coasters.” And NASA turn around and say “That claim sounds a bit farfetched, can you show us some evidence?” To which thegra says “Of course there’s evidence!”. NASA ask him to produce said evidence and thegra says “Try to disprove it ask whoever you want but leave me out of it. I don’t want to get drawn into a long 5 week debate with you. You are the type of organisation that will simply never stop no matter what the other person says or what sources you are shown. I do not have the energy or time to get into a long debate with you here. So kol tov and good bye.”
Hardly credible is it? So why should it be any different when thegra wants us to take the claim that R’ Moshe was mattir issurim d’oraysa seriously without providing evidence?