The fact that mostly Christians show up on pro-life threads, or even that the Christians view the evil of abortion in religious terms, does not make pro-life position depend on religion.
I know some atheists that are pro-life. The Muslims are overwhelmingly pro-life; they are, in fact, our best allies against our own governments at various international fora.
Pro-life is a fundamental issue of individual rights. It is not a religious dogma, like, for example, the Trinity is.
I don't know if you disagree with me on this or not, but I wanted to make it clear anyway. Too many times the proaborts tell me that I want to impose my Catholic religion on them. They do so because they cannot win the argument on its own merits, and they need to obfuscate.
It's true that some atheists are pro-life, but there are a whole lot of believers in God who are pro-life that don't fit into any major faith.
I'm one of them.
Without the right to live then none of us would have any rights at all! It's #1!