You don't really have to read a cheem-o-logy book to understand
the simple concept that :
Only living things can actively renew, grow, and multiply.
Living things metabolise resources and produce energy for their
activities.
Living cells consist of strands of proteins.
etc.
After the sperm merges with the egg, how does it grow and divide
and increase in numbers and even, do the complex cell-division and
cell-specialisation thing?
Answer : It's a living thing.
It IS a living thing right from the point of conception, when the
sperm merges with the egg and fertilisation occurs. That's when
life begins and a foetus starts to slowly develop as that
complicated mitosis, meiosis what-not thing occurs. (Sorry, 80% of
knowledge returned to school lecturers! 
)
I guess folks try to 'soften the blow' and 'lessen the guilt' by
arguing that it is not a living thing, and it's just a 'mass of
cells', and NOT a baby, in the early stages.
That's like saying, a seed that has been planted in the tilled
ground and is slowly undergoing germinating with the shoots slowly
sprouting, is not a living thing. 
It's also like a surgeon looking at your liver when you're at the
operating table and saying, "It's just an organ, a mass of living
tissue and by itself, it's not a living thing!"
