For a more in depth look at Margaret Sanger's thought, watch a 1957 interview with Mike Wallace here (the transcript of the interview is available as well). It's a bizarre interview, be warned. Aside from Sanger's thoughts on human life, marriage and the Catholic Church, Mike Wallace holds no punches, and keeps plugging Philip Morris cigarettes! Weird.
PS - Wallace quotes the Church as saying the sole purpose of marriage is the procreation of children. The full teaching is that marriage's end is two-fold: unitive and procreative, that is, it is for the love and union of hearts and for the fruit of that love and union.... life. In this sense, I feel Margaret's pain when she fights him on this point. It seems in her experience, women were looked on as merely baby-making machines and subjogated by marriage and pregnancy. Clearly the vision is skewed here. For the ideal vision and definition of marriage, read this!