Defense is more than carrying and training with a gun. It is being prepared to fight and survive, which includes having a basic understanding of first aid.
Anyone can stick an adhesive bandage on a cut, but do you know what to do if a loved one is truly hurt? Or what if you have been shot by a bad guy and you are the only thing between him and your family? Could you staunch the wound long enough to provide your family with a few more minutes to prepare or run?
While you don’t need to know everything there is about combat medicine, it would be a good idea to take First Aid and CPR classes. In addition to teaching you what to do if your kid breaks his or her leg, you can learn how to assess a wound, properly dress it and how not to panic in a life threatening situation, which is probably the most crucial of survival skills.
Also, the skills learned will be extremely useful if the world implodes in some sort of apocalypse. And in that sense, you need a first aid kit. I actually recommend multiple first aid kits, compact kits for every vehicle and go bag, with a larger kit for home. When you bandage a skinned knee, simply replace what you used. And while there are many compact kits available from the box stores, you can find everything you will ever need at online retailers like Cheaper Than Dirt, including near military grade trauma kits and supplemental items such as bags of Quick Clot.
Keeping a first aid kit around will make you a hero when your family obtains a small boo boo (yes, I have a small child), and taking a class will make you prepared for most of the injuries you will face.