When does life begin?

I'm pretty sure that most, if not all pro-lifers would answer "at conception." But do you really believe that?
I have seen many inconsistencies within the pro-life movement about the whole "life begins at conception" thing. A major inconsistency is that many people who claim that "life begins at conception" are also in favor of certain types of birth control that are likely to keep zygotes from implanting in the uterus. Implantation and conception are two different things. I'm all for birth control that prevents conception or anything before that, but I'm against birth control that kills another person.
Then there are those people who believe life begins at quickening or at birth, but they will also fight against abortion. Which is something I don't understand. If abortion were not murder, that would take away the whole point of being pro-life.
Why is there inconsistencies and hypocrisy? I have a few ideas. One of them might be lack of knowledge about human reproduction and prenatal development. Historically, people have believed that life begins at quickening (when the baby starts moving), which may have been partly because of lack of knowledge about prenatal development. Another reason could be that people want to have control over when a human becomes a real person, whether they realize it or not. They might choose some random time for the soul to enter the body, or they may choose some random thing that automatically makes someone a person (if they don't believe in souls).
I used to not know when life began. I wanted to say "at conception," like all the other pro-lifers did, but I wasn't sure exactly what that meant. When I learned more about human reproduction, I decided that life begins at implantation. That was probably because I didn't want to believe that certain types of birth control were wrong. Shortly after that, I learned that zygotes have their own unique DNA, which made me begin to question my beliefs.
But knowing that life begins at conception means many things. It means that certain types of birth control are murder. I personally believe that we're going to be with our families in the afterlife, and if life began at conception, it would mean that there would be a lot of people in our family that we wouldn't even know about. For many people, religion has helped them cultivate their pro-life views, which is great. Because my family's religion (which I'm still not sure if I'm going to be part of when I'm older) doesn't have an official stance on when the soul enters the body, it gave me more opportunity to decide for myself when life becomes "important." But after a lot of thinking, I decided that there was no good reason for the soul to enter the body at any other time and that a lot of it was arbitrary.
I have no control over when life begins. Neither do any of us. Or else life would never begin for some people, or it would begin before conception. Why is it that, in a world where we know more about things like prenatal development, that we still fight over when life begins, or when it becomes important? Shouldn't we know this stuff?

(This was also originally posted on one of my other blogs...)