Where did this misconception about abortion come from?

I agree that abortion is wrong in most cases, because it is basically just a tiny defenseless human. The abortion limit is about 20 weeks in Britain (i think). It should be lowered to 12 weeks maximum. After that is just bad. But with growing populations and millions of unwanted, abandoned children i think it would be unwise to ban abortions. The planet is unsustainable at the moment, and women have the right to decide if they want a child or not.