When I say "post only once," I mean submit your comment only once, not that you may not submit more than one comment.  But since comments are moderated, when you submit the comment it won't appear right away.  If you submit more than once, it just clutters up my in-box.  But someone who has substantive contributions to make is, of course welcome to weigh in more than once in a comment thread.   I realize from a few cases now that there's been some misunderstanding about that.   Thanks to those who have been commenting on the interesting thread about the youth of secular moral theory.