Abortion is ok when speaking about "unwanted" children because that term is a very loosely defining term. There are various reasons why someone may not "want" a child. Many people will make the argument that the child should just be placed up for adoption or into the foster system, and that is an acceptable option except for the fact that often times there are not enough resources for the current strain the amount of children in that system place on it. Adding additional children to the system because the parent may not have been able to support it financially, or have been mature enough for it does not mean a child should be placed into a system that also may not be financially sound enough to provide the proper environment for a growing child. This may be a subject where many tread carefully, but abortion should still be considered Ok in this situation.
First trimester abortions, where there is no chance of viability, are acceptable to end unwanted pregnancies and prevent resultant unwanted children that would be born into disadvantaged situations either financially, emotionally or both. That being said, two to three months is plenty of time to make a decision about an elective abortion, and beyond that it makes more sense that abortion be restricted for medical reasons affecting mother or fetus.
Having a child is a choice that should be made after much deliberation and conversation with your partner. The addition of an unwanted child into a family has proven to be a burden more times than not. Abortion is a viable option in preventing the birth of an unwanted child so that the family can wait until the time is right and a child can be born under the right circumstances.
I think abortion should be allowed because if someone is raped, they would be forced to have the baby even though they don't want it, if there was no abortion. Also, the "baby" is not technically alive yet, so you wouldn't really be killing a child, since it is unborn, it did not experience actual life yet. Also, not allowing abortion would increase population and unemployment rates when they grow up, which is not anything close to a good thing. It also has a lot to do with women's rights, since we would be taking away their right to get rid of an "unwanted" baby. This is why we should allow abortion.
Abortion can't be used as an expensive last resort form of birth control, you shouldn't use it just because you were careless and didn't mean to get pregnant. It should only be used for medically justified reasons, not because somebody was stupid and wishes they could undo it. That's unacceptable.
Abortion is killing another human being which defies a commandment from god. The 6th commandment in the Bible is "thou shalt kill." And an abortion is specifically going against that commandment. If someone was just messing around and they wren't smart about it then they're stuck with it. So abortion is not right.