A worst-case scenario would involve a gun, not a knife, and would also involve more than one person. In that case, a knife wouldn't be very useful. A gun would be more useful than a knife in that situation, so why aren't you spending all your time at a firing range and carrying around a handgun? For the same reason I'm not interested in carrying around a knife.
Where I live, I get searched by police at least once a week during my commute. That's just how it is. I've been in maybe 2 situations before where I have been faced with a knife. The math here is as simple as it gets. The risk that would come from carrying a knife makes it unreasonable.
As for being a "fighter," I'm not really interested in your personal philosophies on fighting.
Wow you arent prepared for danger. I think you need to go punch some air and practice your forms.