I was talking about the scene he said swords are designed to kill. Blacksmiths improves their skills so they can make swords that are better at killing than others.
Nami wouldn't be able to use enma and oneshot Kaku. We where if Zoro was a normal swordsman his whole body would be a husk from using enma one time.
The whole point to dangerous or cursed swords are they help swordsman grow stronger by learning to control them. Not anybody could control those type of swords. That what you think is a benefit is actually a curse until you learn control.
If Nami used enma against any character it would take all of her haki and leave her vulnerable. Any enma gave Zoro problems against King and left him vulnerable to attacks at times.