"Most liberals ignore the Church's teaching on abortion as the killing of human life "

This is a gross exaggeration. It is probably more accurate to say that "most liberals" think women should make up their own minds on whether to have an abortion (meaning, abortion should remain legal) but few would say it is not the taking of a human life. Of course it is. But there are times when we  think it is acceptable, or perhaps better to say, excusable,  to take a human life.