Authority has no meaning in this context. A book gives no moral right to any particular act (I hereby declare Godwin in effect; Mein Kampf...?).
The choice is made by an organisation to exclude certain members. Those lines are arbitary, based upon the text that supports them. They could be drawn up across race, sex, height, age, money and eye color. Far as I am concerned, an argument on behalf of any of these factors is an argument for all. I do not believe that to be a moral stance; therefore, I do not believe the concept of eliminating moral upstanding community figures based upon any of the lines that could be created.
And considering the... contribution... of many pastors, I think if a line is going to be drawn, one might want to start with more distinct moral issues.
As far as the transitioning "unbible" to "I didn't say it was not moral", I feel that it must either be claimed the bible is not a moral book and that it exists as an amoral text for this to be valid. Otherwise, it is a moral book, and therefore makes homosexuality immoral. It is either authoritive or it is not; it is either God's word, or it is just another book. If it is just another book, then it, and whole community, is indeed bigoted and cannot hide behind it for excusing their actions or their beliefs. And if it is, then... Well, I would conclude the exact same thing, actually, just including God in their for good measure... but at least under those conditions, one has an excuse for behaviour they would not otherwise accept (as above, simply replace homosexuality with the "card" of the day... like it does every few decades).