"It is wrong to kill an innocent human being, a fetus is an innocent human being , therefore abortion is wrong."
The debate focuses on two distinct issues: (1) whether the human fetus has a right to life and (2) whether these rights equal or override the rights of the mother. A person's stance on this debate may depend greatly on their definition of a human being as opposed to a human life form. If the fetus is considered to be a human being from the moment of conception, then yes termination would be the wrongful ending of a life, but if being human is defined through having a certain level of self awareness and acknowledgment of your person, then the fetus is not yet a human being so aborting it would be as immoral as terminating a cluster of cancer cells, for example.
However, to qualify as a fetus, cells require a separate criteria - fetuses are potential human beings from the moment of conception. Their future contains potential value, in the same way a fully grown human being's does, which leads us on to the definition of killing. Killing could be defined as the cessation of potential to continue life. From conception, the fetus has the potential to continue life, therefore an abortion could be defined as killing. The child who is born and later grows into an adult is the very same being who before birth was in its mother's womb. It is a person earlier as well as later and this is the continuum of human life. Why would something gradually turns into' a person?
It might also be argued that shortly after conception, a unique DNA code is formed which will remain unchanged throughout the life of the fetus and throughout the potential later life after birth. This view bases its argument on science, yet still rejects termination of the zygote as it values the fetus as highly as a born human, in physical terms, because the zygote has the code to develop physically even though this has not yet occurred.