Allow me to say quite methodically ...
A church schism is incompatible with Christian teaching. Let's run it through the good ol' Wesleyan quadrilateral, shall we?
Scripture is quite clear on this point. Over and over again followers of Jesus are commanded to live in unity with one another. It is a prevailing theme of Paul’s. It is inherent in the teachings of Jesus. It is a theme in the Psalms. It is a feature of the most familiar stories of the Old Testament.
And for as long as there have been followers of Jesus, this divinely desired unity has never included uniformity of understanding. Although differences in our beliefs have led to numerous and repeated divisions in the church, Scripture makes it clear that the feet can’t tell the hands to get lost (1 Corinthians 12). We are one. One body, one Spirit, one hope, one Lord, one faith, one baptism, one God now and forever, amen (Ephesians 4).
Unity does not require uniformity, but Christian unity is not equivalent to moral relativism, as some argue. Being united in Christ does not mean that I do not care what you believe, that “anything goes.” Being united in Christ means that when we disagree, we will do so together, in love, as brothers and sisters, unique and beautiful individual members of one body.
Being united in Christ means not only that I care about what you believe, I care about why you believe it. And more, I care about how you treat your neighbor who happens to disagree with what you believe. Being united in Christ means that you should care about what I believe, why I believe it, and how I treat my neighbor, also. Being united in Christ means not that we will agree about everything, but that we will love one another as we disagree with respect and grace.
One who would call for church schism based on disparate beliefs regarding same-sex marriage has decided essentially that what the Bible says about marriage is more important than what the Bible says about unity. And I simply cannot go there. Unity is one of those foundational themes of the entire Scripture - right up there with love and grace and peace and forgiveness.
To make the point through our tradition - Unity is so important to us as United Methodists that we have made it one of the most important roles our Bishops are expected to fulfill. From our Book of Discipline, paragraph 403: “The bishop leads therefore through the following disciplines…,” one of which is “A passion for the unity of the church. The role of the bishop is to be the shepherd of the whole flock and thereby provide leadership toward the goal of understanding, reconciliation and unity within the Church - the United Methodist Church and the church universal.”
This expectation of our Bishops is aligned closely with another Disciplinary statement, namely that “all United Methodists are summoned and sent by Christ to live and work together in mutual interdependence and to be guided by the Spirit into the truth that frees and the love that reconciles” (para. 130).
It really couldn’t be much more clear, could it?
But just to add the lens of reason - how would this split work exactly? How do we know “who’s who” in the two new denominations? Conferences decide? Congregations decide? Pastors decide? And by the way, who gets the pension fund?
And then, once we are two denominations, how are we going to make sure that the people within those churches never have occasion to disagree about things any more? How will we ensure that couples who attend churches in favor of “traditional marriage” never have gay children? How will we guarantee that those who believe marriage should only be between a man and a woman are excluded from congregations who favor “marriage equality?” I hope you see my point here: it just doesn’t make any sense.
Scripture, tradition, reason - all in favor of unity. And lest we forget experience, perhaps we should speak to some of our brothers and sisters whose denominations have split over the ordination of women in the not so distant past about the pain, anger, bitterness, and brokenness that resulted.
And so, for a quadrilateral of reasons, I believe that church schism is incompatible with Christian teaching. And even so, I am hopeful. The Gospel pull toward unity is infinitely stronger than the human tendency toward division. Anyone with a halfway decent sense of eschatology knows that. In that sense, if the UMC does divide, it is only a delay of the inevitable - the feast at the heavenly banquet table in which all of God's children gather together in unity and peace.