Dear Megan Marie,
Your question -- or really your friends' -- is a good and reasonable one and the answer is because anti-feminists, both men and women alike, have kept women from the military, including the draft. One of the consequences of the proposed but now defeated Equal Rights Amendment, which feminists were well aware of, was that women would be required to register for the draft. The argument anti-feminists used most vehemently to prevent the ERA from being passed was that women can't be in the military or in combat, because who would protect our children, etc. Women being required to register for the draft is actually another reason to support feminism -- it doesn't mean that other feminists won't oppose the existence of a draft all together. I hope that helps - keep engaging in those good and challenging conversations.