Abortion.

"It's my body and I can remove what I want from it."

This argument is cold, in my opinion. 

You shouldn't put someone's "will" over someone's life. Pregnancy is temporary, death is permanent.

But that is a moral stance, so we'll debate it another way. Imagine this; in America, if someone goes on your property without permission, you can shoot them (kinda dumb, I know).

You give your neighbor permission to come over for cocktail. As she's halfway through the yeard, you "change your mind" and shoot her. Was that your right, or no? 

To me, it's not. When she entered your property, she had permission. And it's not something, especially when affecting someone's life, that you can remove at any time.

When you had sex, you knew it could cause pregnancy. You laid down, with contraception or not, fully aware that you had a chance of getting pregnant. You consented to that chance.

You CHOSE to take that chance, you made it possible for the sperm to pass (simply by having sex, contraception is 100% effective) and you chose to make it possible.

So by logic, you "gave permission" to the zygote to form, as you made it possible when it wouldn't have been if you hadn't had sex.

You choose that you don't want a baby in the bed, when you're choosing to take that chance or not. You don't choose that you don't want a baby once the baby is already created. One is choice, one is murder, and while it is "your body" (it's really not but we'll address it later) you gave the embryo/fetus to "use it". 

If that makes sense :)