Sorry, title should be "understand". Sigh. The title doesn't show up on the preview.
Oh this one is easy. Being pro-life is too close to be pro-God and you can't cross that fictional wall of separation according to libs. Once you make a judgment that life has higher value than government the libs lose their ideology. Government should be the highest value for a lib...THEN community...THEN individual concerns...(life, liberty, pursuit of happiness) If it ever gets that far.
By valuing life the de-value GOVERNMENT and this is strictly forbidden with the liberal play book.
There is also a smaller element that says young poor uneducated girls can't control their own lives (sex drives) and need the government to provide relief to them in the form of abortion to end the unwanted pregnancy..but the former is much more the case than the later.
Of course all sorts of non-human entities such as corporations, old houses, etc. can be granted personhood in order to support and save them.
Fetuses are denied legal personhood in order to justify their murder. Blacks were denied personhood in order to justify slavery. This is why some pro-lifers equate abortion with slavery.
If you can get a pro-abort to agree that its not a question of when a fetus becomes a human being, but instead when a fetus becomes a legal person, then you may be able to make them realize how completely arbitrary the Roe v. Wade decision was.
You might also scare them into ruminating about how easy it would be for governments to declare them as not being legal persons in some nightmarish fascist fantasy liberals have from time-to-time.
According to liberals, we are supposed to be very concerned about the rights of the terrorists being held at Guantanamo because we could be treated like that in a future Bush administration. But what if aborting fetuses todays is used later as a justification for post-birth-abortions of enemies of the state?