You're one of the last people I would have expected to be concerned with 'fairness' when one of the sides is blatant crackpottery. I suppose you wouldn't have a problem if BHTV invited an astrologer, as long as they paired him up with an astronomer?
What harm is done by bringing on an astrologer? At worst it fail to amuse.
But it's obvious you're not talking about the diavlog's impact on you... you're concerned with the poor, unwashed masses who might actually be left to form their own opinions from the available information. Well, that's very nice of you, but I don't think it's unreasonable to believe that it's safe to expose people to views which might be labeled as "crackpottery" by some.
I declare this Open Thread open for discussion of Less Wrong topics that have not appeared in recent posts.