I don't think its right under any circumstance to exclude a certain group from activities due to their sexual orientation. This has a lot to do with morality and what is right and what is perceived as pure judgment and what is right and wrong. It is WRONG in my opinion to exclude a human being from any sort of activity as such, because of a chosen lifestyle.
The Boy Scouts of America are an organization that is charged with helping young men to develop skills that can help them throughout their lifetimes in multiple situations. By excluding homosexuals, it seems that all that would be taught is that people should not be treated equally. There is no evidence that homosexuals commit sexual crimes at a higher rate than heterosexuals, and that means that there is no reason to fear having a homosexual either as a Boy Scout or a Boy Scout Leader. I believe that there is no justification for the Boy Scouts to exclude homosexuals from their organization.