From the current platform (italics are mine):
Freedom of Association and Government Discrimination
Individual rights should not be denied, abridged, or enhanced at the expense of other people's rights by laws at any level of government based on sex, wealth, race, color, creed, age, national origin, personal habits, political preference, or sexual orientation.
We support repealing any such laws rather than extending them to all individuals.
Discrimination imposed by government has caused a multitude of problems. Anti-discrimination laws create the same problems. While we do not advocate private discrimination, we do not support any laws which attempt to limit or ban it.
The right to trade includes the right not to trade -- for any reasons whatsoever; the right of association includes the right not to associate, for exercise of this right depends upon mutual consent.
End excerpt from the platform.
The Boy Scouts are a private organization and should be free to admit or not admit whoever they wish.