ubiquitin: A freilichen Purim!
To answer your queries, I do not accept as “torah misinai’ what is said by some of the people you mention. It has never been conclusively proven why Rav Goren’s psak should not be accepted. As Avi K points out, this particular “hetter’ is used with great abandon by chareidi Poskim today- invalidating thousands of Geirim on the same basis. Rav Goren only meant it as a psak in that one instance whereas chareidi Poskim -today!- use it to “passel” thousands of good Geirim. That, by definition, reeks of politics.