(Which would put even unfertilised eggs and skin cells on the same level of an adult human being. So to avoid ridiculous comparisons such as those, you'd have to value something like consciousness, or at least the level of consciousness than humans possess, more than simply being "human".)

Actually one would just have to define personhood as being a property of alive individuals of species of higher inteligence... wich acording to the very definiton of "individual" (an unfertilized egg isnt gonna grow on it's own as a full human being.. at least not on the real world.) would completely eliminate such ridiculous comparisons.

But if one would choose consciousness as the absolute consideration for personhood... then newborn humans are just fu%ed up... acording to the latest philosofical rumblings of peter singer and daniel dennet... they have no self consciousness... wich ultimately delimitates moral significance so...
let's just kill babies at will.