The union of a human egg with a human sperm starts the beginning of an entity that is surely human. We call human entitys persons.
Alright... I'm going to push back on this.
I understand your belief, and I respect it. But I also disagree with it.
At conception, that zygote has none of the components that we think of as a person, aside from genetic code. I don't think it's reasonable to think that two cells with some DNA in it is a human being - it has the potential to become a human, certainly, but it isn't really one yet.
As it develops, it gets closer to human, but it spends a while pretty much being a tadpole. At the earliest stage of development, all vertebrates look the same, and have the same developed parts - spinal cord, and the start of some organs. As it continues to develop, fish and birds and mammals start to diverge - preliminary limbs form that show differences by class.