Abortion is being portrayed as if it were something in shulchan sruch, where the magen avrohom says one thing and the elya rabba another, and rav moshe ignores them to deliver his own psak. Rav moshe deals with rav yaakov emden(an acharon who actually isn’t given as much weight as the kreisi uplaysi, for instance), but there aren’t that many sources on the subject, much less an established precedent as if they’re in the rishonim and nosei keilim. Rav moshe was, as i said, literally on the level of learning of an early acharon, as anyone can see from his dibros moshe.
In psak, rav moshe often argues with achronim, he was criticized by some who didn’t recognize his gadlus in learning, like the author of maaneh le’igros, who had his own issues… zionism, Holocaust denial (as in, denying the causes thereof), etc..