Julian Savulescu echos Elizabeth Harman with his solution for embryo ethics:

There are other values which can account for our polar opposite moral norms, attitudes, practices and laws. This is a value to controlling our reproduction, in deciding how many children we will have and when to have them. “Go forth and multiply” – but there is a limit. Early human life has value when it is a part of plan to have a child. The reason why Challancin was wrong to kill his girlfriend’s baby was because she wanted to have that baby. Challancin is more like a drunk driver who recklessly kills an innocent child than a doctor who performs an abortion. Destruction of embryos is a moral crime when parents wanted them. It should have been Miller and Parrish who decided the fate of their embryos, not the Chicago clinic.

Here is the solution to the puzzle of our conflicting attitudes: embryos have special moral value when they are part of a plan to have a child, or at least desired by the people who made them. Embryos do not have special moral value when they are not desired by the people who formed them.