I don't think it matters whether you are Christian or not, really.
There's no disputing that a life which did NOT exist prior to the uniting of an egg and a sperm DOES exist after that.
Whether that life is entitled to the same civil protections that we give human beings is obviously debatable. Reasonable minds do come down differently on this issue.
But the vast weight of historical thought, religious thought, and philosophical thought until the 19th century was that abortion was murder after quickening.
On the other hand, it wasn't until the 19th century that scientists really understood conception, anyway.
Life existed before... What you argue is that potential life is equal to life... It isn't...