@ Abge.. I wasn't going to get involved in this, but here goes..
My religious beliefs inform my stance on a select few policy issues. Society agrees on a certain set of standards which are enforced as laws. Some of these laws rightly have a moral basis. Killing another human is against society's moral code (as well as my Christian religious code). We can agree on this secular law because our moral codes align on this issue. Thus having a moral basis for a law can be a good thing.
On the flip side, having a moral basis for a law isn't always a good thing. An aethiest could have a moral code that killing animals is wrong and therefore eating meat is just as bad as murdering a human, while a religious nut could have a moral code that anyone who doesn't believe as he does should be put to death. Laws in support of these examples would be outrageous as I'm sure we can both agree.
So having a moral basis for pursuing a policy decision is not in and of itself, inherently good or bad, would you agree? From a secular view of policy making, rejecting a policy stance simply because it has a moral basis, is ludicrious, just as accepting all policy stances based on a moral code is horrendous idea.
So the real question is how do you determine which policy stances are worth consideration?
I'll leave that question open ended...
Instead I'll simply address the particular case at hand, why my religious views are relavent to why I take a stand on this issue:
As a christian, my moral stance on abortion is tied to my moral stance on murder. Both of these are based on what the Bible says about God's stance toward, life, taking life, murder, the value of children, the oppressed, the helpless, and even in a select few cases, those yet unborn. As a case in point, Jesus and the Old Testament repeatedly talk about defending the fatherless and widows. The unborn are the least able to take care of themselves of any category of people. In addition, statistically, at least in my community, (I don't recall the national rate) the majority of abortions occur in situations where the to-be father is not present (the fatherless).
Because the unborn are defenseless and have no advocate, and because I also believe them to be human individuals from the time of conception (based on Scripture), that is why I take a policy stance on abortion. In this case, separating the two removes the heart of the issue for why I am taking a stand in the first place.
Because my religious beliefs include a basic belief about what a human life is, I can't set aside my worldview to keep a completely secular view of this issue when I believe it to be an issue of an individual having their right to live legally taken revoked by societal 'norms.'
@ Obi: Are you asking how a person's religious beliefs on heaven and hell (and where an aborted baby would end up based on those beliefs) would allow them to oppose abortion?