 How do you know that what you call "kefira" isn't really a better understanding? Your argument is that refusing to treat opinions as so sacred that they are above criticism leads one to doubt the validity of those opinions. That's almost certainly true; so what? If the only way an opinion can be sustained is to put it beyond question, then it's probably not a very sound opinion. One whose faith is so weak that he can't permit others to question his views is not only a kofer (since he knows that his beliefs won't survive scrutiny), but a hypocrite as well. 