Why? I figure there's three different groups involved. First, there are people who believe that gay men are much more likely to be child molesters than straight men. I've seen arguments on both sides, but this group doesn't seem to be a majority in and of itself. Second, there are people who believe that homosexuality is either immoral or at least highly undesirable, and they do not wish their sons to be set an immoral or undesirable example by adult leaders and thereby become influenced towards such behavior themselves. The concept that homosexual behavior is 100% innate, and is not a learned behavior, does not have majority support in the U.S.
I belive this to be quite close to the truth, and also, since I belive both stands to be ilogical, I belive that eventually, as public opinion changes, so will the BSAs opinion. I would assume that the racist position of the BSA in the 1910-20's had public support back then, too? BTW, you mention three different groups? As I read your post, you only mention two?