[myrrh]

It means that in typical circumstance it will grow the be a human, and therefor we should not prevent it's opportunity to do so.

Let me clarify this- Before you can be a human, you need to be an embryo. The embryo is alive and going to grow into a human. You speak about 'potential' like the embryo can grow into a cat or cow, and we need to wait and see to make sure that it is a human. The embryo inside a human is a human embryo!

You said: "People who hold this argument need to be reminded that the same future life could well have been lost had contraception been used, or (perhaps more appropriately for them) had abstinence been practised at that crucial moment in time."

This is true, but the fact is that at the point of discussion, that being about embryo's, the above is irrelevant because conception had happen, and now you have a living organism inside the female.