I never asked you to prove God's existence. It's impossible to prove so since he is unobservable. Similarly it is impossible to prove his nonexistence. Empirically, the question of God is irrelevant and indeterminate.

Also, correct, theory is not proof. Did someone say anything to the contrary?Theory only models chunks of the universe in a way that is consistent with observations. The big bang theory doesn't seek to explain the cause of the big bang, only to model the universe as having had a big bang.

Now, regarding abortion... The issue of abortion is not over whether the fetus is distinct from its mother, but that whether it should be considered life in the morally meaningful sense. A fetus is alive in the biological sense, but not necessarily in the sense that a mind (also known as a soul) is present.

Consciousness, the key factor of a soul, is like God: unobservable. One cannot prove that anyone is conscious, except oneself. In order for inter-human morals to matter, one must assume that others do have a soul as well. Some people might like to think everything has a soul, such as rocks and plants, but I personally find that paranoid.

Empiricism seems to correlate mind-like behavior with the brain, so I consider that a reasonable criteria: Abortion doesn't bother me unless a brain has developed, because otherwise I will assume that like rocks, it has no soul. It may still have no soul even after the brain has developed, but I'd rather be safe than sorry (but again, not paranoid).

Now, it is understandable that a religious person might think differently on the issue. They think of souls as not originating from the brain, but rather as some thing entirely independent from the body. I consider this a possibility (and I would love for it to be true), but as consciousness cannot be observed, this is unknowable. Anyway, if theists consider this true, then it becomes very uncertain as to what point in time this soul attaches to the body.

Also, assuming that abortion does occur before the soul becomes active or attached to the body, there's another moral issue: Is it wrong to prevent life (soul, not cells) from starting, or just to cancel it once it has started. I personally have no qualms with interrupting a process that will naturally lead to a soul coming to life. I only consider it wrong to kill that soul once it has already come to be. Of course, there are many who will disagree.

I don't think that this is an issue that is likely to be settled any time soon, given the difference between the two views, and at the same time, the unwillingness for either side to compromise.