I think the GB are taking some things for granted here...
They are supposing that the single brothers in the Cong are attractive, whereas in reality there are more likely to be nampy pamby mummies boys with no personality.
Also they have supposed correctly that yes the brothers want to have sex as soon as possible. But have not thought that the sisters want the same. The GB seem to imagine congregations full of single, submissive, blushing sisters with no sexual desire at all. Whereas in fact the sisters want to get laid just as much as the brothers. Since single brothers are in short supply who cares weather they are MS or not?