An embryo is a stage of being a human. As you say, you were an embryo yourself. It's only because we can't see it that we feel it's not human enough and can be killed. The thought of not being "human enough" doesn't bode well in our history, especially around the 1940s timeframe.
A spermatozoon is a stage of being human… so is an “egg cell” but nobody is forcing people to allow them all to develop into humans! And no… the nazi example has nothing to do with it (and I say it as a person whom all grandparents got sent to concentration camps by nazis)
This argument at its core is trying to justify at what stage of development this is considered human enough to protect. I think it’s a similar line of thinking as eugenics.
