"But I don't think you need to be religious to be pro-life."

Perhaps, but take religious views out of the argument and it becomes very fragile.

We have to be irrational about breeding. Otherwise only people with nothing interesting in their lives would have children and we would be on our way to CM Kornbluth's "Marching Morons" world. Lactating mammals feel an intense protectionism toward their young that is known to be hormonal.

And, again, most fetuses are not viable. Only 30% implant and many miscarriages come later.