UPDATED 11/27/11 to correct typos and make some adjustments in response to comments on Romans.
At the heart of the Stone-Campbell movement was a calling “to restore Christianity to its original purity and power,” in which Disciples historians have recognized “the significant role of American religious liberty.”  This section explores how this calling led the church founders to believe that (1) church doctrine and human tradition had crowded out the simple, true Gospel of Jesus Christ and (2) a particularly destructive manifestation of this perversion of the faith was the exclusion of some from the Body of Christ. These themes are evident not only in the works of Thomas and Alexander Campbell and Barton W. Stone, but also in the work of John Locke, a particularly influential philosopher for the church founders.  In Locke’s A Letter Concerning Toleration he wrote,
Whosoever requires those things in order to ecclesiastical communion, which Christ does not require in order to life eternal, he may, perhaps, indeed constitute a society accommodated to his own opinion and his own advantage; but how that can be called the Church of Christ which is established upon laws that are not His, and which excludes such person from its communion as He will one day receive into the Kingdom of Heaven, I understand not.
Note both the notion that human doctrine could corrupt the teachings of Christ and that the corruption leads to exclusion.
The Stone Movement’s important Last Will & Testament of the Springfield Presbytery addressed the corruption of the Gospel with human tradition. Stone’s Christians willed “that candidates for the Gospel ministry henceforth study the holy scripture with fervent prayer, and obtain license from God to preach the simple Gospel, with the Holy Ghost sent down from heaven, without any mixture of philosophy, vain deceit, traditions of men, or rudiments of the world.” Even more graphically, at the beginning of the Observations written to accompany the Last Will & Testament, the Christians asked, “How often even among us, has he been crucified afresh, and put to an open shame; pronounced powerless, dead, and buried among the rubbish of human tradition?” This sentiment was not held only by the Christians. In Alexander Campbell’s Declaration and Address, the first declaration is that the Disciples were forming a religious association “for the sole purpose of promoting simple evangelical Christianity, free from all mixture of human opinions and inventions of men.” A pithy summary can be found in the popular slogan: in essentials unity, in non-essentials liberty, in all things charity. 
In place of human tradition and creeds, the founders encouraged adherents to read Scripture for themselves. In the Appendix to the Declaration and Address, Campbell explains that the Reformers “propose to patronize nothing but the inculcation of the express word of God–either as to matter of faith or practice;–but every one that has a Bible, and can read it, can read this for himself.–Therefore we have nothing new.” Likewise, the Christians willed in the Last Will & Testament “that the people may have free course to the Bible, and adopt the law of the spirit of life in Christ Jesus.” Indeed, as mentioned above, when Barton W. Stone was required to accept the Westminster Confession as a part of his ordination into the Presbytery of Transylvania, Kentucky he would not accept the creed without qualification.  Stone records in his autobiography, “I went into the Presbytery, and when the question was proposed, ‘Do you receive and adopt the Confession of Faith, as containing the system of doctrine taught in the Bible?’ I answered aloud, so that the whole congregation might hear, ‘I do, as far as I see it consistent with the word of God.’ No objection being made, I was ordained.”  Or, as another slogan goes, “Where the Scriptures speak, we speak; where the Scriptures are silent, we are silent.” 
As a natural consequence of rejecting creeds, Stone and the Campbells both rejected tests of membership.  In the introduction to the Declaration, Campbell put it this way.
We are also persuaded that as no man can be judged for his brother, so no man can judge for his brother: but that every man must be allowed to judge for himself, as every man must bear his own judgment;–must give account of himself to God–We are also of opinion that as the divine word is equally binding upon all so all lie under an equal obligation to be bound by it, and it alone; and not by any human interpretation of it: and that therefore no man has a right to judge his brother, except in so far as he manifestly violates the express letter of the law.
It is perhaps its direct link to rejecting exclusion that makes the story of the Communion token so popular. It is undisputed that the Seceder church to which Campbell belonged in Scotland required that before receiving Communion members must first qualify for a Communion token.  Some have suggested that when the plate came to Campbell he threw his token upon the plate and compared “[t]he ring of that token, as it fell from his hands [to] the ring of Martin Luther’s hammer on the door of the Wittenberg cathedral.”  Others report the incident more as an internal moment in which Campbell quietly refused Communion in personal protest.  In either case, rejecting exclusion was an essential part of Campbell’s vision.
These principles strongly argue against discriminating against Christians based on sexual orientation or gender identity. First, having the same sexual orientation and gender identity as the majority of Christians in a particular congregation is not an essential. Walter Scott identified what was essential for membership as the “golden oracle” recorded in Matthew 16:16, namely to confess that Jesus is “the Messiah, the Son of the living God.”  And even if Scott’s formulation is too narrow, the absence of any discussion of sexual orientation or gender identity in Scripture demonstrates that these traits are not essential to being a follower of Christ.
This leads to the second point; the Bible is entirely silent on sexual orientation and gender identity. There is literally nothing addressing same sex couples getting married or adopting children. To be sure, the Bible references acts of sex between people of the same physical sex. However, the Scriptures do not consider the notion of a loving relationship between two people of the same physical sex. Consider Romans 1:26-27.
Because of this, God gave them over to shameful lusts. Even their women exchanged natural sexual relations for unnatural ones. In the same way the men also abandoned natural relations with women and were inflamed with lust for one another. Men committed shameful acts with other men, and received in themselves the due penalty for their error.
Paul describes abandoning natural relations and being inflamed with lust. Nothing in this description seems remotely related to the couples at Chalice Christian Church raising children together in committed lifetime relationships. More importantly, that it was in fact unnatural for some women to have relations with men–that people have sexual orientations that are not necessarily determined by their physical bodies–was an entirely foreign idea to the authors and the early readers of the Scripture. Thus, the Scripture is silent on sexual orientation. The silence of the Scripture on this topic argues for accepting Christians of all sexual orientations and gender identity.
Third, exclusion of Christians based on sexual orientation or gender identity is a mixture of human opinions and inventions of men with Christianity. As discussed above, one’s sexual orientation and gender identity is not a topic of Scripture. Rejecting people who are gay, lesbian, bisexual or transgendered has become a creed proposed by some Christian churches. It is a social issue–like whether a man may take multiple women as his wife–but is not a Christian issue.
Finally, the principle of religious liberty supports accepting Christians without regard to sexual orientation or gender identity. Furthermore, the principle supports being public about the church’s acceptance. Perhaps at sometime in the future a congregation’s declaration of being open to and affirming of Christians regardless of sexual orientation and gender identity will be as proforma as an employer’s declaration of being an Equal Opportunity Employer. Until that time comes, however, the absence of such a declaration amounts to de facto exclusion. Such a membership test cannot be harmonized with the principles of the Stone-Campbell movement.
Of course, this is not to say that the movement’s founders would have literally accepted gay, lesbian, bisexual or transgendered Christians. How the movement’s principles have directed the evolution of the Christian Church (Disciples of Christ) is the topic of the next section.
 M. Blowers, Douglas A. Foster, and D. Newell Williams, Stone-Campbell History Over Three Centuries, in The Encyclopedia of the Stone-Campbell Movement at xxii (2004 ed.).
 See, e.g., D. Duane Cummins, The Disciples: A Struggle for Reformation (2009 paperback ed.) (noting the significance of Locke for the Disciples founders and that Alexander Campbell referred to Locke as “The Christian Philosopher”).
 For a thorough investigation of the origins of this slogan see Hans Rollmann, “In Essentials Unity”: The Pre-History and History of a Restoration Movement Slogan, available at http://www.mun.ca/rels/restmov/texts/unitas/essrev.html
 Paul M. Blowers, Creeds and Confessions, in The Encyclopedia of the Stone-Campbell Movement at 252.
 Barton W. Stone, A Short History of the Life of Barton W. Stone, in The Cane Ridge Reader at 30 (1972 ed.)
 Cummins at 119.
 Id. at 68.
 See, e.g., Leroy Garrett, Campbell, Alexander, in The Encylopedia of the Stone-Campbell Movement at 118; Cummins at 52.
 Al Maxey, Tale of the Tossed Token: Campbell’s Last Communion Coin, available at http://www.zianet.com/maxey/reflx148.htm
 Garrett at 118; Cummins at 52.
 Blowers at 254.