Foster was one of the long-time members of the American Anti-Slavery Society where he met radical abolitionist Abby Kelley, his future wife, and traveled the church and anti-slavery meeting circuits with Douglass, Garrison, Redmond, Phillips and others, giving speeches.
"In the annals of the antislavery movement, the throwing of rotten eggs is as commonplace as the tossing of custard pies in vaudeville. Garrison told his wife of one such episode in Syracuse that November: 'Our friend S. S. Foster then took the platform, and . . . made his favorite declaration . . . that the Methodist Episcopal Church is worse than any brothel in the city of New- York. Then came such an outbreak of hisses, cries, curses! All order was at an end. Several ruffians rushed toward the platform to seize Foster, but were not allowed to reach him. The tumult became tremendous. Several citizens, who were well known, attempted to calm the storm, but in vain. Rotten eggs were now thrown, one of which was sent as a special present to me.'"
Frederick Douglass, William S. McFeely, pg. 102