Notice that the Marine only fought when he had no other option. According to other news reports on this incident that I've come across, the Marine tried to escape first while shouting "Fire! Fire!" but he had to slow down to retrieve the pocket knife from his packpack, which is when the muggers caught up with him.

I wish all cases involving self-defense were this clear cut and had such happy endings. Also, I hope someone gives this Marine a decent folding knife that he can carry on his person --it's no fun rummaging through a knapsack for a pocket knife when your life is in danger.