The go-to shabbos poskim, like shmiras shabbos kehilchasa, rabbi ribiat, rabbi simcha bunim cohen, etc…all say that you can’t tear letters, even though it’s mekalkel. Can anyone bring a source about rav moshe’s alleged heter? I haven’t seen it, and i think it would have been more commonly quoted if it were true.
Rav ovadia yosef holds it’s muttar entirely, and i know many sefardim who rely on this. For ashkenazim, I don’t know of any poskim who explicitly allow it.