Come-outer is a phrase coined in the 1830s which denotes a person who withdraws from an established organization, or one who advocates political reform.
The term was first applied during the Second Great Awakening to a small group of American abolitionists who dissented from religious orthodoxy, who withdrew from a number of established churches because the churches were not progressive enough on the issue of abolition. A come-outer would not join a church which held a neutral position on the issue of slavery, and he would not vote, or run for office, or otherwise take part in a government that let slavery happen. The phrase was derived from the Bible verse, II Corinthians 6:17 which read "Wherefore come out from among them, and be ye separate, said the Lord, and touch not the unclean thing; and I will receive you."
William Lloyd Garrison was an influential Boston abolitionist who founded the New England Anti-Slavery Society and the American Anti-Slavery Society in the early 1830s. Garrison advocated an immediate end to slavery, rather than a step-by-step process working through the political system. In 1832, he printed an anti-slavery tract called Thoughts on African Colonization which included the "come out from among them" verse from the Second Epistle to the Corinthians, and a quote from a recently deceased Reverend Doctor Thomson of Edinburgh: "To say that we will only come out of the sin by degrees—that we will only forsake it slowly, and step by step... is to trample on the demands of moral obligation..." At the New England Anti-Slavery Convention in 1836, Garrison proposed that only churches willing to help fight slavery should be considered "the true and real church of God." This was viewed by many as too divisive, so other means were tried until the 1837 convention when a resolution was adopted urging abolitionists to leave unresponsive churches, "to come out from among them and be separate." Garrison's radical ideas defined a strong split within the anti-slavery societies, and Garrison was abandoned by all but a dedicated core group of like-minded abolitionists. The Boston-based group of reformers began to be called "come-outers".