It is, but then, how else do organizations which hold anti-gay bias interpret things? To them, being gay is the most egregious of sins, worthy of ostracization and condemnation... and some would say even death. You can see it in their belief that to be gay is to be a sexual predator. To be gay is to be immoral, and therefor anyone not straight is not to be accepted. This is how they view things. It's really quite sad, although, not unexpected considering who runs the BSA.
The name of the "Boy" Scouts might seem inherently sex-discriminatory in that only those who are of the male sex are permitted to join whether a leader or scout. There are many organizations that sets requisites on membership including the AARP (over 50), NAACP (African American), or the NEA (American Educators). These groups all receive funding; however, the requisite on membership serves a compelling state interest, and therefore, the requisite is permitted and treated differently depending on the type of requisite under the Due Process Clause of the 14th Amendment.
There are three levels of scrutiny:
Rational Basis - This includes groups such as occupation or age. The standard employed when these groups rights are in question is whether or not that restraint of freedom has to serve a broader COMPELLING INTEREST, not LEAST RESTRICTIVE MEANS.
Heightened Scrutiny- This includes groups that have had some discrimination in our society, yet observe less prevalent and/or less severe forms of discrimination currently. This would include women.
This is an medium between LEAST RESTRICTIVE MEANS and COMPELLING INTEREST.
Strict Scrutiny - This category includes African-Americans, Hispanic-Americans, Native Americans, American-Muslims, American Jews, other minority racial/religious groups in America, as well as, LGBT-Americans. These groups must have observed extensive history of discrimination based on inherently possessed qualities.
Laws must use LEAST RESTRICTIVE means in achieving a state interest whenever these groups' freedoms are in question.
THUS, the gender/sex-based issue I posed initially posed, whether gender-discrimination can be employed, is that, yes, since it falls under the intermediate level of scrutiny. The scouts can easily make a good argument that the scouts are preserving an interest by maintaining an all male organization since women are not severely affected by the existence of the group.
However, when it comes to gay youth and adults, the state should adhere to the strict scrutiny standard since LGBT people have been and continue to endure substantial discrimination; thus, the boy scouts must use LEAST RESTRICTIVE MEANS; by which, disallowing membership is very restrictive, and therefore, is a breach of this standard and is not constitutional.
The Supreme Court, ruled contrary to my explanation several years ago, when LGBT-members were considered under the RATIONAL BASIS TEST; however, the Court has changed their stance on LGBT, reclassifying them under HEIGHTENED/STRICT Scrutiny depending on which Justice we are talking about. With the DOMA cases soon to be decided, we will find out if LGBT people will be under the strict standard more concretely. IF SO, then the Scouts would likely be required to end ban on gay members, adults and youth.