Can Michael Shermer Be Good without God?

Fellow atheist/skeptic PZ Myers drops this hand grenade on Michael Shermer's credibility, who wrote a book along the lines of the title of this post.

I’ve got to do what I’ve got to do, I can do no other. I will again emphasize, though, that I have no personal, direct evidence that the event occurred as described; all I can say is that the author is known to me, and she has also been vouched for by one other person I trust. The author is not threatening her putative assailant with any action, but is solely concerned that other women be aware of his behavior. The only reason she has given me this information is that she has no other way to act.

What do you do when someone pulls the pin and hands you a grenade? by PZ Myers