That's not true. There are dozens of natural means of abortion, using physical or herbal methods. They are not quite as effective as modern medical means. And in many cases, they aren't as safe either. But women have been performing abortions since before civilization. Abortion is quite natural.
The fact that it's behavioral instead of internal doesn't make it any less natural. Behavior is natural.
Horses can miscarry at will. And they do if they aren't permitted to mask paternity by having sex with multiple males. That's an abortion.
On the latter point, I agree.