Volvie,
I could present links to the positions to the rabbis I mentioned but YWN does not permit outside links. You will have to find them yourself.
Rabbi Sacks is probably the most brilliant Jewish mind alive today and he should not be dismissed as casually as you do.
Rabbi Goren’s position that one can pasul a conversion does indeed has no precedent in halachah, but that has not stopped the “Gedolim” from accepting it and in fact taking it far further than Rabbi Goren would ever have imagined.