On abortion, doesn't the issue arise as a borderline case amongst people who agree on certain basic principles? I know that people who disagree on abortion seem miles apart, but think about it. They agree;
1) In cases where the child is already born, it should be a crime to kill the child if it is, say, an inconvenience (which children invariably are).
2) We should be concerned about the quality of life as well as about life itself.
The question is whether the case of a fetus is in any way relevantly different from the case of a born infant. No one questions the value of life or the value of the quality of life. They just disagree about whether the fetus is relevantly different from infants and toddlers. But there seem to be agreed-upon moral truths that both sides accept without question.
Sometimes we get so busy arguing about the ethics we disagree about, that we forget the huge number of moral judgments on which most all of us agree. But of course it would get boring in ethics class if we were to argue about, let's say, the ethics of serial murder.