When Does a Human Receive a Soul?

Questions about when a human receives a soul and how to respond to someone who rejects science, reason, philosophy, and objective morality in her effort to defend abortion, saying that pro-lifers just want to control women.  

• When does a human receive a soul? In the zygote stage, the cells haven’t differentiated yet, and some become the placenta, but the placenta doesn’t have a soul, so why would the zygote?
• Should I give up trying to persuade someone who rejects science, reason, philosophy, and objective morality in her effort to defend abortion, saying that pro-lifers just want to control women?