It's simple. Yeah, it may be your body, but does that mean people should be able to cough into your mouth? It's their body, but it's harming you.
But now, my body my choice is being used for abortions, and abortions harm no one else other than the child (which wouldn't have a brain yet), so as long as you don't go around, trying to get pregnant, nothings wrong with abortions.