And consider that low-income women are also far more likely than their wealthier sisters to be smokers. Some 25% of women living BELOW the poverty level are smokers. Somehow, even with their limited disposable income, they find ways to purchase cigarettes, which, on a monthly basis, actually cost them more than birth control pills. These women have revealed their preferences, and birth control pills don't seem to be high on the priority list.
Unless you oppose contraception on moral grounds, what you've just stated is a reason to give birth control to these women for free, not the opposite.