I hate to use Claudish here, but "postnatal" and "dead" are quite load-bearing here :) Clinically dead? Coma? Born human baby, but with anencephaly - expected lifespan is days, and there's literally no brain - but, well, are they a person? Ask 1000 people - and I'm betting we'll get a nice bimodal distribution.

I take your point that a human walking around a city will - out of that 1000 responses - hopefully get 990+ of "yes, a person" - but that will start to degrade quickly once you hit boundaries.

And the less said about dehumanizaion - untermensh and that entire line of thinking - the better.