Perhaps you think that the crucial difference between a fly and a human blastocyst is to be found in the latter's potential to become a fully developed human being. But almost every cell in your body is a potential human being, given our recent advances in genetic engineering. Every time you scratch your nose, you have committed a Holocaust of potential human beings. This is a fact. The argument from a cell's potential gets you absolutely nowhere.

p. 30 - Letter to a Christian Nation (2006)