When kiba was fighting sakon and ukon or whatever the siamese twins were called on the sasuke retrieval mission, he setup an exploding knife trap. It NAILED the guy, and the only reason he lived was some crazy ass "Lets merge together and that lets me ignore my lethal wounds" move. In the very first adventure, iruka takes vicious injuries from kunai and shuriken from mizuki, again the only reason he survived was naruto using his plot armor to protect him from the finishing blow. Iruka was dead meat and virtually crippled. When haku put zabuza in a false death state, kakashi, a highly experienced ninja, believed that needles were an effective tool for murdering powerful ninja. Kunai shuriken and swords are treated as clearly lethal threats in naruto no matter how hard you try to pretend they arent just because noone specifically in the main cast dies to them.