The passage of the Fugitive Slave Law of 1850 caused considerable conflict among the Unitarians of Boston. The Fugitive Slave Law required that runaway slaves be returned to their so-called masters. It also criminalized anyone who aided or harbored runaways. The legislation was enacted in an effort to preserve the union of the Northern and Southern states in the lead-up to the Civil War. It was opposed by some Unitarians as immoral and supported by others as a necessary compromise to prevent the nation from splitting apart over the conflict about slavery.
One of the most prominent opponents to the Fugitive Slave Law was the minister Theodore Parker (1810-1860). Parker was a Transcendentalist and one of Boston's leading social reformers. He began his career as a Unitarian minister, but his radical theological views caused many of his Unitarian ministerial colleagues to ostracize him by refusing to exchange pulpits with him. In 1845 he left the Unitarian Church of West Roxbury to become minister of the independent Twenty-eighth Congregational Society of Boston. His congregation grew rapidly and at its peak as many as three thousand people gathered for a Sunday worship service. This represented almost two percent of the population of Boston at the time! Some of those who attended were among the most prominent anti-slavery and social justice activists of their time, including Senator Charles Sumner, educator Horace Mann, and abolitionist William Lloyd Garrison.
Parker called repeatedly for non-compliance with the Fugitive Slave Law. In a sermon he preached immediately after the passage of the law, he said, "It is the natural duty of citizens to rescue every fugitive slave from the hands of the marshal who essays to return him to bondage; to do it peaceably if they can, forcibly if they must, but by all means to do it."
Parker's views were not held by those in leadership positions within the American Unitarian Association. One notable supporter of the Fugitive Slave Law was Ezra Stiles Gannett (1801-1871). Gannett was a founder of the Association, serving as its first Secretary and later its President. He also served the Federal Street Church in Boston, first as William Ellery Channing's assistant and later, starting in 1842, as Channing's successor. In the 1830s Gannet had cautioned Channing against speaking out about slavery, knowing that his senior colleague's views were not shared by many powerful members of the congregation.
Gannett reluctantly supported the Fugitive Slave Law because he felt it was necessary to preserve the Union. Perhaps more importantly, many of the officials charged with enforcing the law were members of his congregation. According to the abolitionist Samuel J. May, Gannett had stated, "he should feel it to be his duty to turn away from his door a fugitive slave, —unfed, unaided in any way, rather than set at naught the law of the land."
Gannett's feelings were shared by other members of the Unitarian establishment. Parker publicly took Gannett to task for his support of the rendition of Thomas Sims, a man who had escaped from slavery in Georgia and resided at the time in Boston. In April of 1851, Sims was kidnapped on the streets of Boston by policemen and returned to slavery in the South. Unitarians from Gannett's congregation played a role in Sims' kidnapping.
In a public address to mark the one-year anniversary of Sims's adduction, Parker accused his fellow ministers of celebrating "the sacrament of kidnapping." Shortly beforehand, at a ministerial meeting, Parker had lambasted Gannett for "calling on his church members to kidnap mine." At the same time, Parker claimed, "I have in my church...fugitive slaves. They are the crown of my apostleship, the seal of my ministry." He told his fellow ministers, probably hoping that they would pass the message along to their congregants, that he would use violence to prevent the seizure of other fugitive slaves. He is famous for claiming that he wrote his sermons with his pistol by his side. Parker went on to assist many other fugitive slaves, and ultimately provided money to support John Brown's attempt to start a slave insurrection in Virginia, defending a slave's right to violence as a means of liberation. After a long illness, he died in 1860, with no show of sympathy from the Boston Unitarian establishment.