"one can have respect for the person without necessarily having any respect for the they sometimes utter"

A good start may be not to call it "gibbering nonsense" to the person, or to resist the temptation, and not get on the topic at all:)

"Why have a belief at all?

If you don't know something for sure, just leave it open in your mind".

Well, I guess that would rule out much of life, that one does not know for sure?

That would include "stuff" like a belief that your wife is beautiful....at least until her "looks" are put through some type of test to certify she really does or doesn't fit the universal mold for such a belief, (if such a test exists).