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The threads of this discussion all point in one direction: progressivism is stronger the more people who are committed to it. It does no good to exclude all believers because of the vileness of a subgroup. Though an atheist, bi-sexual, commie, I have at least two good friends who are deeply christian, one the daughter of a minister and the other a lutheran pastor. They are committeed to protecting the earth, stopping war, pushing social justice, fighting greed, etc. On the side of the angels, so to speak. Progressives/lefties cannot afford to push such people away. When one of them announced to me that he was 'pro-life' (his code for anti-choice) we had a long and useful discussion about how many on the 'pro-choice' side were also 'pro-life' in the sense that they do feel abortion is a sad, tragic event in the lives of those who have to resort to it. (strangely, many in the anti-choice camp do not understand this about those who are pro-choice). No one is 'pro-abortion' any more than someone is 'pro-divorce' or 'pro-adultry' just because they feel divorce and adultry shouldn't be illegal. This friend is also in favor of birth control and good, full, sex ed in school. There is a great deal of middle ground to be found in supporting public policy that would reduce the number of unwanted pregnancies (free birth control, comprehensive sex ed, etc), or create an econmoic environment where people can afford to have a child (good, cheap child-care, good jobs, etc.).
There is less middle-ground on the question of gay rights. At least that is largely a generational issue, and we just have to wait around a while for a lot of people to shuffle off this mortal coil, or at least stop voting.