There is only one problem with your numbers, there are many churches who have said that homosexuality is acceptable. They will not drop the boy scout troops.
How many churches denominations in America say it is acceptable? And their membership numbers?
It is not about churches - its about congregations. The national church may say it is ok, but individual congregations may balk.
You gotta remember that the BSA is a volunteer-led organization. The individual congregation [ie: the pastor] may say it is ok, but he still has to have volunteer congregants to lead the troop.
This is no different than individual congregations revolting over birth control, ordination of women, etc.
There is a schism brewing on the horizon for the BSA ...