I'm sorry to post three times on something that might not be related... but I have a thought experiment.
If someone loses a leg, they are no less human than people with two legs. On that we can all agree. If someone loses an eye, they are no less human than those with two eyes. You can lose almost any part of your body and still be a fully fledged human, deserving of all rights under the sun. You could, as have some soldiers, very, very sadly, lose all your limbs and almost your entire body, but if your brain is still there, you're still human. I mean, you wouldn't scorn a US or Australian or any Veteran of any nationality for that matter, just because they've lost parts of their body, would you?
But if someone loses a brain.... are they still human? You can lose almost your whole body but if your brain is still functioning, you are no less you. Your memories, personality, humour, wit and ability to feel pain and happiness are all still there.
Now what about someone who loses 90% of their brain? What about someone with CJD or Huntingtons - whose brain has mostly been irrecoverably destroyed by disease, yet retains juuuuuuust enough neural tissue to sustain autonomic functions. What about someone who has all their limbs, but is brain dead? Are they still really human?
I'd argue no. What gave them the spark of humanness is gone. Irrecoverably gone. You might be able to, in the future, regrown parts of the brain, but the unique combination of neural connections and patterns is irretrievably lost.
If your family member is brain dead or mostly brain dead.... would you stop life support? They can't feel anything. They're permanently not-conscious. They're not even unconscious because being unconscious implies the existence of a dormant conscious. If they have no frontal lobe, no occipital lobe, if 90% of their brain is just........ GONE, and gone forever, you have to ask yourself: are they already dead? The flesh lives on, but the mind is gone. And if the mind is gone.... is there any point to the life of the individual in question? Are they even still an individual if they have no higher or even lower brain functions? Blind, deaf, not even capable of thought - I know that I wouldn't consider myself still alive in those circumstances.
So if you agree with me that a brain dead patient is, for all intents and purposes, already dead, then is a brainless embryo really human?
And if you contend that the brain dead patient IS still human and alive because his or her heart is still beating and the cells are still dividing.... well technically an egg is a living cell. So is a sperm cell. Yet we don't call masturbation (sorry for the reference) mass murder and we don't call a period a murder either. And if you say "well, it's because those cells don't have a full set of chromosomes).... well, what about cell cultures? I've killed more HeLa Cells than you could shake a stick at. They were just as "alive" as a brainless embryo. Was it wrong to kill the HeLa cells? And if you say 'well, an embryo has potential to become a human', well, I'd argue that "POTENTIAL to become a human is not the same thing as BEING a human", just like how an acorn seed could BECOME an acorn tree, but you wouldn't call it an acorn tree.