Final answer:
Elizabeth Cady Stanton's belief in reproductive rights and birth control, though championed later by Margaret Sanger, was very controversial, even more so than her advocacy for women's suffrage. The correct answer is option d.
Step-by-step explanation:
Reformer Elizabeth Cady Stanton's most controversial belief was related to birth control. At a time when notions of womanhood largely centered on motherhood and domesticity, advocating for birth control was profoundly radical and challenged the very foundation of women's role in society as seen by many. While suffrage was a principal focus of women's rights activists, Stanton and others like her also fought for other rights for women, ranging from property ownership to higher education. Among the founding goals of the National Organization for Women (NOW) was not the decriminalization of birth control, which indicates the sensitivity and controversy of the subject during the early feminist movement.
The issue of suffrage was certainly central to Stanton's activism, and she was key in initiating the Women's Rights Convention at Seneca Falls, where the 'Declaration of Sentiments' was read, demanding suffrage for women. Yet, Elizabeth Cady Stanton also challenged other oppressive social norms and legal constraints of her time. The notions Elizabeth Cady Stanton advocated regarding reproductive rights were indeed part of a larger conversation on women's autonomy, which Margaret Sanger later became heavily associated with when she led campaigns to provide women with information on birth control and opened clinics to provide reproductive health services to women. Sanger's work, although occurring later than Stanton's initial advocacy, illustrates the burgeoning movement towards women's autonomy, a movement in which Stanton played an essential part.
Despite the focus on suffrage, it was the candid discussion and activism around topics like reproductive rights and birth control, led by figures such as Sanger and supported philosophically by earlier activists like Stanton, that remain among the most controversial aspects of the women's rights movement, showing that while Stanton's belief in the necessity for women's suffrage was critically important, her broader work to champion autonomy in all facets of life for women was also deeply transformative and controversial.