It’s very necessary, especially in the case of a woman who is pregnant and has a medical problem and continuing the pregnancy may harm or even kill the woman. And the woman already has kids. It would be unfair on the existing kids for her to sacrifice herself for a fetus as they would face losing their mother.
If a woman is raped, continuing the pregnancy may be too traumatic for her so she may choose to abort in order to move on from her horrific experiences. You could argue that the unborn child is innocent and so it would be wrong to abort the child, but it’s the woman’s choice and she may be in a bad mental state over her traumatic experience, rendering her unable to adequately care for her child, causing the child to suffer.
She may not have enough money to support the child; I believe it’s unfair to knowingly bring a child into a life of poverty and struggle.
If the fetus is severely disabled, I also believe it would be unfair to birth the baby and subject it to a difficult, short, painful life.