manta49, some thoughts:
1. It is easier for most people to do violence with firearms; less training is necessary, and less luck is typically necessary - this is much the same reason why the crossbow supplanted the long bow.
2. In the hands of a skilled person, a knife could be the more effective tool, depending upon intent. (If the intent is to take down a target with minimal noise, for instance.)
3. While this is a gun forum, many of us probably carry knives, too. Some of us are also into martial arts training. It would not surprise me if quite a few TFLers participate in knife and martial arts forums.