Well said, but as usual I would put it much more strongly: Anyone whose
relationship with you is so fragile that expressing your honest beliefs
might jeopardize your friendship is no friend. Such a relationship can
be of no benefit to you, and if your honesty ends it, then it has saved
you time and energy that you might more profitably invest in a healthy
relationship elsewhere.
Likewise, if your friend has some psycological need for your approval of
his ideas, your acquiescence is no benefit to him; it only serves to
feed his neurosis.
Of course, this applies mainly to voluntary relationships. There are
certain externally-imposed relationships like close family, roommates,
and business associates that may require different treatment. I tend to
deal with these mostly by treating them as obstacles to be worked around.
I do not loudly proclaim my atheism to my Baptist minister uncle, but
nor have I had to deny it--I simply don't let our conversations turn to
that. I simply acknowledge that my time is better spent developing my
voluntary relationships (which, happily, include my parents, my sister,
and my rommate (though not all of their spouses, alas). I have never
needed to express a belief I don't hold, though I have often had to bite
my tongue and quietly move to a different conversation.