That is what this boils down to. If you can not confidently, without hesitation, answer yes, then you have no business standing in front of the counter. If the answer is yes, then you should feel an obligation to ensure you are proficient in the skill required to employ that weapon effectively and efficiently. "Train like you fight, fight like you train".
With the time the USMC (and ultimately, the USA) invested in the training to ensure I had a firm grasp on marksmanship fundamentals and all the time I spent honing those skills over the years, I feel it an obligation to keep those skills sharp, and ready to act to defend my fellow citizens should I ever be placed in a situation to do so.
This includes while traveling on my FJR.
Can I drop the hammer on the bad guy when it comes to it?