There has been a lot of talk of late in my church, the UMC, about schism. How it is a sin, etc. etc. etc. This talk has usually come up in conjunction with the discussion of the ironically titled One Church Plan to resolve our difficulties, which rather than resolving them devolves them down to the Conference and local church level. So, perhaps it would be useful to talk about what the term schism actually means, theologically and ethically speaking. First, a little historical perspective.
Denominationalism is a post-Reformation notion, largely conjured up by the Protestant movement. It is not a Biblical idea, nor will you find its equivalent in the literature of the early Church Fathers. And when there has been talk about schism in the early church (for instance when the Orthodox and Catholic traditions went their separate ways), the issues were mainly theological (the filoque clause), rather than ethical by and large.
Schism was, and is caused, when one group within a church decides that it can no longer adhere to the orthodoxy or orthopraxy that is the de facto official position of a church. On this showing, those who are advocates for gay marriage and the ordination of self-avowed, openly gay persons would be the persons creating the schism today in the UMC. They simply refuse to accept what the Bible says about the nature of marriage and appropriate sexual behavior for various reasons, and as a result refuse to accept what the UMC Discipline says on these same matters.