-Opinions of aesthetic similarity to a newborn are irrelevant just as size, communication abilities, and self-awareness are.
-Someone on life support in a coma may respond to communication or demonstrate self awareness but that doesn't change them into something other than a human, after all.
-Of course you can kill something that's not human. All animals can be killed, regardless of their species.
-"Developed cognition and self awareness" aren't requisites for being human according to any dictionary I've seen.
-You are correct in observing that we're not living in the middle ages. It's a wholey irreverent statement to the topic at hand, but it's accurate nevertheless. Gold star.