trisher, the woodcraft groups operatively differently than guides or brownies, this much is easily understood. It's very different to ask children whether we wish to have mixed dorms, than to have a girls group go away,, totally unaware they have a boy dressed as a girl in their midst. If it must happen, surely parents and children are entitled not only to know but to express their wishes . Woodcraft encourages and operates with full participation, so does our Brownie group.
It sounds as though your dislike of 'uniform' organisations leads you to conclude that the woodcraft way is the best. My daughters and their friends did both. They loved Brownies and were keen to maintain the expectations of behaviour expected there.
One size doesn't fit all. I would be very unhappy if my 7 year old daughter was confronted by a boy in the dorm/shower etc, if she hadn't known that a boy had been allowed to join them.
There is such a lot of evidence that confirms girls benefit hugely from single sex organisations, even schools. Mine went mixed primary and comprehensives, I wouldn't have wanted any other experience for them but - I do understand why the parents of some girls choose a single sex education.