Some people are really smart about one subject... say guns for example. They're very smart about guns. Everything about them from ballistics, to gunsmithing, legal issues, you name it.
Some of those people don't have a clue about life in general. They have no social skills b/c they're life is absorbed in guns. They cant even maitain a healthy family relationship b/c they clearly lack the means of fulfilling their family roles and duties as a family member.
These people are generally absolutely worthless people in life, but they know a shitload about guns. If you've got a problem with guns, they can help you fix it. You might not like their style, but that doesn't matter. Pay no attention to their 'delivery' and only to their 'content'.
Kind of reminds me of the people who valet park my cars everyday. They sure know a lot about cars.