On this issue I'm not a propertarian. I simply view it as a right to life argument and that all killing is wrong, and that's usually where I end. However, I recently got into a debate with a pro-choice propertarian over the issue of abortion. It was civil, although fierce, but I came to a new property rights pro-life view.
First, we must define a few terms and throw out some arguments that have no basis or simply make no sense.
What is life? This should be a fairly obvious answer: any organic organism which is not dead (a definition can be found here or here). However, there is obviously something that separates us from plants and that is sentience, awareness, or conciousness. This is what makes life all worthwhile and what makes it so scary to lose. Now, animals are also sentient, but our amount of awareness is much greater, which is what separates us from them. But why am I talking about this? Because there are a few arguments that can be dispelled by this definition on both sides, mainly, "when does life begin?"
Many Christian pro-lifers want to assert that life begins at conception because that's when a soul enters the body. This, however, is for me an inadequate argument as there is no scientific or conclusive proof, only the dualist argument, that there even is a soul. And even if there is, there is no way to prove when it "enters" the body, if it "enters" at all.