It is natural for your body to do all kinds of things that we consider negative, preferencially. Vomiting is usually something your body does in self-defense. It's a perfectly natural and good and properly-functioning response. Doesn't change that you can still vomit yourself to death, and that we prefer to avoid it by getting flu shots, for example.
It's also natural for your body to go into menopause, but the problem with this is that in a state of nature, for many women, it means your days are very numbered. So for these women, we treat them, because they can have another 30 or 40 years of life if we do so. Menopause is perfectly natural, and there's a very good reason why it can deterorate your health. You won't produce healthy offspring at that age. The same happens to men, we're learning.
Our bodies do all kinds of things that can hurt us, but are there for very good reasons. Things we may not wish to happen. So we stop them. Same with pregnancy. We have been aborting pregnancies since the very eariliest civilizations. Abortion is, in fact, part of our natural behavior. There are even other species who abort in their own way.
Furthermore, why isn't it an attack? Who cares if it is natural and part of your own body?
Any time your body or mind becomes endangered by something against your will, that can be qualified as an attack. Unwanted pregnancy is most certainly an attack, both physically and mentally.