According to the "Boy Scouts of America [BSA] National Council Legal Issues Website and Blawg" (which was "created on behalf of the Boy Scouts of America"), "Boy Scouts of America believes that an atheist or agnostic is not an appropriate role model of the Scout Oath and Law for adolescent boys. Because of Scouting’s methods and beliefs, Scouting does not accept atheists and agnostics as members or adult volunteer leaders." And apparently your sexuality is your own business so long as you don't discuss it, but being "openly homosexual" makes you persona non grata in BSA's eyes.
If BSA was truly a private organization that received no government support in the form of preferential access to public lands or facilities, I'd say they were welcome to whatever membership policies they wanted. The fact that the Church of Jesus Christ of Latter-day Saints (the Mormons) sponsors more Scouts and Scouting units in the United States than any other organization would make me instantly wary of BSA anyway.
Since BSA's leaders believe it inappropriate for me to be around impressionable youth, I've decided to spare them the horrors of dealing with my money, which must surely be tainted. I wish I didn't have to tell my nephews who are Scouts that I won't buy their nuts or popcorn or whatever they're peddling this week, but when they're a bit older, I'll make sure they know why I won't buy them.