This changed in 1833 when crowds of people, called 'abolitionists', joined the American Anti-Slavery Society en masse, with William Garrison drafting the society's "Declaration of Sentiments" that, drawing on the American Constitution, demanded immediate emancipation for slaves, condemned slavery as a sin, and recommended that its repeal be brought about through moral persuasion rather than through violent acts. The American Anti-Slavery Society set about disseminating themselves in every city, town, and hamlet, circulating pamphlets and broadsheets in order to publicize their opinions. Their activities were largely helped by evangelical ministers and churches, and it was in this way that activists such as Frederick Douglas became aware of the movement and active on its account. Southerners attempted to hinder the movement, but it continued unabated. Two categories of anti-slavery activities may be made. There were moderate antislavery...

The other, more radical group constituted so-called 'immediatists' (such as Adam and the Gag band) who demanded not only unconditional emancipation for slaves but also civil rights on a par with White Americans.
The murder of Elijah Parish Lovejoy, a white man and editor of an abolitionist newspaper, particularly enraged the anti-slavery movement and lent swell to the rage against slavery. It was also the defining factor that turned many northerners into immediatists demanding an immediate end to the slavery system, not only in the North but everywhere else too.

Source

Maier, Smith, Keyssar, & Kevles. Inventing America: A history of the United States.