Flip your own framing around - aren't there likely boys who would have preferred the Girl Scouts coded activities, and being disallowed from membership is therefore also an unfair dis-opportunity?
Yup exactly. Same as all the "feminist" groups campaigning to disallow trans women from such groups, usually using the excuse that they'll get assaulted by the "really just men" trans women a la "won't somebody please think of the children!" when the incidences of this happening is almost 0 comparatively.
Turns out some are allowed to have special clubs, but others not so much. And we only have societal perception of women to blame; the thing they're relying on for all this "they need their own space to protect them" is demeaning, imo. Besides the fact that the majority of victims of crime are male (and before someone points out that the majority of criminals are also male - did you know that's a sexist statement to make? It's judging an entire sex by the actions of individuals).