Our troop's underlying purpose is very similar to that of the BSA as a whole, "[to] prepare every eligible youth in America to become a responsible, participating citizen and leader who [makes] ethical and moral choices over their lifetimes by instilling in them the values of the Scout Oath and Law." This sounds great to parents, but to this day I do not believe we have ever seen a boy drawn to Scouting in order to become a "model citizen," and not because he wanted to go camping and play with fire and knives (by "play," I mean, "learn to use responsibly").
In general, our main purpose can be seen as teaching a wide range of skills to boys in order to build character and foster responsibility and independence. The term for the skills we teach is "Scoutcraft."
Just a little side note, some may ask why I chose the ".ninja" top-level domain. The Oxford dictionary gives the informal definition of "ninja" as "a person who excels in a particular skill or activity," whereas the original ninja was trained in many skills, like the Scout.
Just for fun, I compared some traditional "ninja skills" (ninjutsu) with the Scout's skills (Scoutcraft):
The remaining skills are martial arts related and are not taught directly by the Boy Scouts. These mostly deal with edged weapons, and the closest we get to that is through a knife or tomahawk throwing activity at some camps (not very common, though). The BSA officially does not approve offensive martial arts; however, "defensive" arts such as Tai Chi, Aikido, and Judo are "approved Scouting activities" but must be supervised and taught by a qualified instructor. It may be possible to use such a martial art in completing the Sports merit badge, but the counselor must approve it.
Interestingly, there was among the original 14 Merit Badges (called Badges of Merit back then) a Master-At-Arms merit badge. Wherein a Scout would prove mastery of three of the following: single stick, boxing, jiu jitsu, wrestling, quarterstaff, or fencing.