Why is poison use "evil"?

[RoboEmperor]

Man v.s. Man, sword and shield v.s. sword and shield, this is an honorable fight that pits the two man's strength and skills to their absolute limits to determine who is the better.

Poison = Cheap shot. It robs its opponent to pit their strength and skill against you since a slight scratch will kill them, or if you put it in their food. Therefore it is evil.

Not in d&d where poison is easily resisted, but this is the gist of good/evil mentality/morality in medieval times.

"Evil" people use things that let them kill things vastly stronger than them using cheap shots like poison against an army general or political manipulation to jail/exile/execute said general forever. "Good" people challenge them to a 1 on 1 duel.