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Firstly those who say there is no difference between a sperm and an embryo are so obviously wrong that I won't bother to explain.

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I'm not sure who said there is no difference. I agree, there is a difference. They both have the potential to be persons, though. As does every cell in my body. But, it's much more likely that an embryo will become a person than that a sperm/egg or other human cell will.

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I have no problem with those who say that killing an embryo is not murder as long as they would say the same thing about killing an embryo kept alive in a futuristic incubator.

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If that futuristically-incubated embryo does not yet have a functioning cerebral cortex, than I would say it is not a person, and therefore killing it would not be murder.

Obviously, I'm disappointed that this is the only response to my questions, but I should have expected as much. The "Raving Atheist"'s blog shows that he is very intelligent and rational, yet a lot of people could not get him to explain his rationale for claiming an embryo is a person.

I think, in the end, the fact is that there is more evidence to support the belief that personhood requires a functioning brain. This is what medical science uses in determining if and when someone is dead. Obviously, an embryo does not have a functioning brain, so if it were on the operating table, a doctor would declare it legally dead.