Matt gave an overview of his scepticism here that moral status is attained at conception, citing Don Marquis' transitivity of identity argument placing moral status beginning at segmentation (14-21 days post-conception).
Matt is agnostic as to whether moral status is acquired at conception but argues that unless there are good reasons for thinking the pre-segmentation embryo does not have human moral status, it is seriously immoral to destroy it. Agnosticism like Matt's is not a good enough reason, so Matt opposes the destruction of embryo's from conception despite not being convinced such entities possess human moral status.
I intuitively felt the argument was flawed but could not articulate why or how which was frustrating - lack of philosophical training really bugs me at times. Baylor University's Alexander Pruss has very kindly written a rebuttal of Marquis's argument after I asked him to help me to either understand the force of Don Marquis' continual identity problem or give me an argument to overcome it.
Matt plans to look at it in detail this weekend but for those of you following the discussion on the matter back in the original thread it originated in I thought you might like to look at it too. I think Pruss' argument is very good and it encapsulates the threads of the objection I had towards it in my own mind but lacked the ability to formulate clearly.