What are Macbeth arguments to himself against killing Duncan?

* The king is a good and just ruler. Macbeth states that Duncan is "A king / So clear, so perfect, and so just" (I.vii.17-18). He goes on to say that the king has "no art in that" (I.vii.18), meaning that Duncan is not a tyrant or a cruel ruler. Macbeth also notes that Duncan is "most royal" (I.vii.19), which suggests that he is a legitimate ruler and a respected figure.

* Killing the king would be a sin. Macbeth states that "this even-handed justice / Commends the ingredients of our poisoned chalice / To our own lips" (I.vii.10-12). In other words, he believes that if he kills Duncan, he will be punished for his crime. Macbeth also states that he is "too full o' th' milk of human kindness / To catch the nearest way" (I.v.17-18). This suggests that he is too kind-hearted to commit murder.

* The consequences of killing the king would be too great. Macbeth states that if he kills Duncan, he will "wake Duncan with thy knocking. Ay, would thou couldst!" (II.ii.35). This suggests that he believes that killing Duncan will not be easy and that he will be haunted by the crime for the rest of his life. Macbeth also states that if he kills Duncan, he will "put rancors in the vessel of [his] peace / Only for them to bear with me to ruin" (II.ii.36-37). In other words, he believes that killing Duncan will only lead to more violence and bloodshed.