I think the 19th century just provided a culmination of factors such as wider access to education for women, the emancipation movement and later granting suffrage to black males, a more progressive attitude in general with industrialization, and the move even further towards an individualistic society.
Women gathering in groups to support emancipation for the slaves began to question why they weren't seeking it for themselves. Also when the men went off to war it was up to the women to run the homes and businesses. The boom of the woolen industry in New England employed women outside the home and outside of traditional "women's work." In a warrior society it was expected for the men to go off to war as needed and the women to run the home but particularly in America the nation hadn't engaged in full-scale warfare since the Revolution. Those women were testing their teachings against their experience and coming up short.
It's also very hard in cultures where the emphasis is on the group to stand up against that group. It takes great courage to risk being an outcast.