What if, as a second class scout, you have completed the requirements for camping and swimming and received the merit badges for such. Shouldn't you be signed off on First Class requirements #9a, b, &c (from swimming MB #3) as well as requirements #4a and b (from camping MB #8c&d)? If not, then in theory, a second class scout must perform a line rescue two times to be signed off on both the First Class requirement and the merit badge? I just don't see this as double dipping but as requirements defined by the merit badge.
The requirements for the merit badges are much more de