I used to know a woman who was married to an abusive husband, and when she finally found enough courage to divorce him, she found that she was 3-month pregnant (as a result of being forced to have a sex with him). She couldn't bear the thought of having a child of the man she loathed, so she decided to have an abortion. Whether you agree with her decision or not, you couldn't possibly call her a murderer.

We all do what's best for us and any potential children under our own individual circumstances at the time. Many people who have made their own personal choices have talked themselves into feeling those choices were so right (for them) that they become a bit judgmental out of protection of their own psyche for their decisions. That's all I can come up with for the reasoning.

Why one should live life to one’s own satisfaction. The opinion of others about one is irrelevant. Even if they are right.