He became an abolitionist in 1835, after seeing an antislavery meeting at Utica broken up by a mob.
These differences led to the organization of a new National AntiSlavery Society in 1840, and to the formation of the "Liberty Party" (q.v.) in politics.
He was essentially humane; and it is worthy of notice that he was in favour of the abolition of slavery, while humane men like his friend Lord Sheffield, Dr Johnson and Boswell were opposed to the antislavery movement.
In 1815, while living at Saint Clairsville, Ohio, he organized an antislavery association, known as the "Union Humane Society," which within a few months had a membership of more than five hundred men.
He was bitterly denounced by slaveholders and also by such non-slaveholders as disapproved of all antislavery agitation, and in January 1827 he was assaulted and seriously injured by a slave-trader, Austin Woolfolk, whom he had severely criticized in his paper.