When a new bayo comes from the factrory, it is sharp, not Chris Reeves Sharp, but sharp enough to cut paper.
People are told not to sharpen them for a variety of good reasons.
-They are not trained how to sharpen knives
-There is only so much metal there so once you get a herd of humans vyeing for the sharpest bayonet, you are going to have a bunch of people running around with toothpicks mounted to their rifles.
-With the kind of abuse the knives are subject to, IE tightening the wiring for revetment, and the fact that they are no space age material, Whats the point in it being sharp? It wouldnt last for long, and every good soldier has a good knife on them. Sharp or dull, I still would not want to be on the receiving end of a bayonet, and neither would any other sane person.
Most people use their bayonets for abusive tasks that they would not use a better knife for. There has only been one bayonet charge since the 2nd world war. (For which the most recent VC was awarded) Its just a primitive capability to not forget. There's no rocket science or light saber sharpness required. You run, you fight, hopefully, you are there to keep on going the next day. How would a sharper bayo help you there? Better to spend your time PTing.