Edged-weapons range.
When a projectile weapon is not an option.
it is psychologically easier to kill with an edged weapon that permits a long stand-off range, and increasingly more difficult as the stand-off range decreases. Thus it is considerably easier to impale a man with a twenty-foot pike than it is to stab him with a six inch knife.
This is an interesting observation: The physical range provided by the spears of the Greek and Macedonian phalanx provided much of the psychological leverage that permitted Alexander the Great to conquer the known world. The psychological leverage provided by the hedge of pikes was so powerful that the phalanx was resurrected in the Middle Ages and used successfully in the era of mounted knights. Ultimately the phalanx was only replaced by the advent of the superior posturing and psychological leverage provided by gunpowder projectile weapons.
It is also easier to slash than to stab. Stabbing has it's sexual overtones. For a bayonet-, spear-, or sword-armed soldier his weapon becomes a natural extension of his body - an appendage [...] To reach out and penetrate the enemy's flesh and thrust a portion of ourselves into his vitals is deeply akin to the sexual act, yet deadly, and is therefore strongly repulsive to us.
Of course the thought of getting stabbed isn't much fun. "The thought of cold steel sliding into your guts," says McKenna, "is more horrific and real than the thought of a bullet doing the same - perhaps because you can see the steel coming." ...in Rwanda, where the Hutu tribesmen made their Tutsi victims purchase the bullets they would be killed with in order to avoid being hacked to death.
John Keegan's landmark book The Face of Battle makes a comparative study of Agincourt (1415), Waterloo (1815), and the Somme (1916). [...] Keegan repeatedly notes the amazing absence of bayonet wounds incurred during the massed bayonet attacks at Waterloo and the Somme. [...] "...there being no evidence of the armies having crossed bayonets at Waterloo." By World War I edged-weapon combat had almost disappeared, and Keegan notes that in the Battle of the Somme, "edged-weapon wounds were a fraction of one per cent of all wounds inflicted."
I already mentioned that at the end of a bayonet charges soldiers just turned their weapon and used the butt of their rifles on the enemy - despite their rigorous training. "Prince Frederick Charles asked a German infantryman why he did this. 'I don't know,' replied the soldier. 'When you get your dander up the thing turns round in your hand of itself.'"
...the resistance to killing with the bayonet is equal only to the enemy's horror at having this done to him.
Another German infantryman told: "I stabbed him through the chest. He dropped his rifle and fell, and the blood shot out of his mouth. I stood over him for a few seconds and then 1 gave him the coup de grace. After we had taken the enemy position, I felt giddy, my knees shook, and I was actually sick."