[klipt]

Assuming those 1000 embryos belonged to e.g. 100 cancer patients who were subsequently rendered infertile by chemo, the choice really comes down to, kill one child, or effectively sterilize 100 cancer patients by removing their option to have biological children.

You could rephrase the problem as this: you have a sterility gun that will fire 100 times. You can direct it into a crowd where it will permanently sterilize 100 random people. Or point it at one 4 year old, who will be killed by the accumulated 100 shots. Which is more harmful?