Thanks for everyone's response. It seems like the consensus is that I
should use vapor barrier. However, I haven't received any good
arguments for other than the reason I mentioned.

My carpenter specializes in renovating old homes. He says that he's
never taken apart a house that did not have vapor barrier and had
problems with mold, but he's taken apart many homes WITH vapor barrier
and seen lots of mold and wood rot.

I'm not sure who to believe.

Jack