I have been the teaching assistant for a course entitled 'Theology of the Welcoming Church'; we have had wonderful diverse groups of students, from traditional/conservative to liberal in background, multi-denominational in affiliation. It always promises to be a good course and provide dialogue for better understanding even if it does not resolve the issue for all in one way or the other. Just for the record -- I am trying to stay as objectively neutral as I can be; I have my biases too, but given that I don't have the answers either (how do I reconcile scripture and tradition with the experience of people I know?) I guess mostly what you'll read here are my fumblings in the dark.
Boswell's book 'Christianity, Social Tolerance, and Homosexuality' is an early scholastic contribution to the history of how homosexuality has been treated by the Christian church establishment from the beginning of the Christian era to about the fourteenth century. It won the American Book Award for History in 1981. Boswell (now deceased) was a professor at Yale; I have a friend on faculty at the IU Music School who went to high school with him.
Perhaps Boswell's argument can be summed up fairly easily in that, through examples in contemporary literature and records (legal, theological, literary, etc.), homosexuality was not recognised in the same way that it is today, and therefore that it also was not condemned in the way that it is today by much of the church. Friendships and close relationships often developed into sexual ones; these were not considered unusual. There was a variation from culture to culture, but the widespread condemnation of homosexuality didn't begin until thirteenth and fourteenth centuries, when tolerance (not only of this, but of religious opinions in general) ceased to be the rule, as the church (a dominant military, political, and social force as well) attempted to consolidate power.
Boswell's research is extensive and impressive, but his interpretations have remained hotly debated for the 20 years since this book was first published. One scholar-friend of mine who knew Boswell said that his psychological motivation for writing the book (this is a theme that was not designed to win favour in academia at that point in time) was to confront the Catholic church, in which he as a gay man did not feel welcome. And, there is probably some truth to that. Knowing that framework, it is interesting to re-read passages to see where objective scholarship slips into subtle reframing.
Nonetheless, this book provides an excellent historical framework, and cannot be ignored in the current debate. I encountered this book first many years ago when my church was undergoing a discernment process, and it was useful in many ways. Boswell claimed to know of isolated communities and continuing strands where such tolerance continued to the present. He promised on a few occasions (at least semi-publicly) that he would reveal these in the next volume, Same Sex Unions, produced many years later, and an even more controversial text.