Any argument you can use to justify an abortion can be used to justify any other immoral act, including sex slavery, rape, human experimentation, genocide, the seizure of property by the state, anything...
Why?
Firstly, there are too many people on the planet. Why would you want children to be born into a situation which isn't good?
The only reason you have a problem with abortion is because you feel that the fetus has a personality already. You can see that you have a conscience, what you might call a soul and because of that you don't want to see an unborn baby die.
However you don't think a cow has a soul, so you couldn't give a damn about whether it dies or not.
If you're not religious and you don't believe in a soul, and you don't think a child has a conscience when it's unable to survive on its own, then why would it be a problem?
Also, 75% of fetuses are aborted naturally by the body before the woman even knows it's there. If you believe in God, then this is God's doing. He made humans, he made the reproductive system and he made it when most fetuses die. So, why is it okay for God to abort 75% of fetuses, but then it's a problem for humans to abort fetuses?
Also, how many people who have a problem with abortions DON'T have a problem with war, executions, guns, and all the other stuff?