I think the debate stems mostly from the imperfections of our spoken language.
What is a human? Is it any biological organism that is genetically identifiable as homo sapiens? Is it our bodies? Our minds, hearts and 'souls'? When asked to draw a "human", a man will sketch a head, a torso, a pair of legs, two arms. On the most basic level we see this shape everyday in our lives - that is what we all subconsciously equate the word "human" with.
Is it all there is to it? Shouldn't we be focusing on what makes us human as the philosophers would see it? Creativity, spontaneity, our thoughts and dreams - everything that goes on in our brains? Consciousness?
There will be more and more debate in the coming years as the concept of what is "human" will come under fire. Technological advancements, medical innovations and strong AI will throw our preconceptions under a train and force us as a species to reconsider, for better or for worse.
Do you see how the abortion debate stems from different understanding of the same concept? There is no right and wrong.
Dictionaries rule over our minds.