Lesbian NORCs

The New York Times has a story today about another naturally occurring retirement community (NORC):  lesbians aging in communities they formed several decades ago, at a time when the general population was much less welcoming to gays than it is today. Some of these communities now include the (gay) children of original members.  I was struck, however, by the fact that the communities do not permit straight family members to live there as well.  Is such a dogmatic approach necessary?  I guess it's no different than over-55 communities that do not permit younger family members to come live with the residents.