As a farmer's daughter living in a farming community for whom farming is a very big deal, I want to point out that the "using birth control is like farming" metaphor just doesn't work.
While there is not a tidy bijection between women's bodies and Mother Earth, real flesh-and-blood farmers "husband" the earth. Yeah, they, um, farm it, i.e. push it toward production. Even the hippies with their green manure and their heirloom inheritances and their Native American rhetoric. Because, look: farmers want their soil to generate an abundance, year after year after year. They tend the soil, they care for the soil, they even love the soil, but they do not wander about at the edge of their fields wringing their hands, wondering if maybe this year they ought to let the weeds take over. And they do not ever think that maybe it's time to sow salt in their fields, rendering them infertile, because they have more crops than they can handle. (HAHAHAHA! That one is my favorite. Like any farmer anywhere wouldn't know what to do with a surplus of crops.)
Please, everyone in the world, please, please, please stop using farming as The Thing that Proves whatever it is you want to prove. Farming doesn't work that way. No, it really doesn't. Leave the fields to the farmers and the women to their husbands. Life and the creation of life isn't easy poetry; it can't be neatly bent to this or that idea of what's right. The poetry is simply correct. It is up to us not to use it, but to become it.