While it's unfortunate, there are a lot of people who just aren't interested in the reasons why someone would carry a gun. (It is sad really, because in today's day and age, it should be clearly obvious why someone would carry a gun.) Some of these people aren't interested in "being educated", they just know that they don't like it, and therefore others shouldn't be carrying. their true problem isn't that, "your carrying a gun", but is actually their own fear. Until they are ready to address that fear, they won't listen to reason.
My mother once asked me the same question when she saw me OC'ing at their house. She is an intelligent woman whose husband has had guns in the house since they were married. She knows all about the evil that can happen in society. Therefore, I knew that she wasn't interested in "why" I was carrying. I knew that the real reason she asked was that she just didn't like it. My response was to calmly and lovingly look her in the eye and say, "why do you have a problem with it?" Until people can face their own fears, they aren't going to easily listen to logic and reason.
Your explanations to your friends for "why you carry?" were good, and you handled it well. The comparisons were spot on.