Does Macbeth know that the murder of Duncan is a terrible action in Shakespeare's Macbeth? Does he see it as a right action?

Macbeth knows that killing Duncan is wrong, and the only thing that justifies it is his greed.

Macbeth is aware that killing Duncan is a terrible deed.  He wants to kill Duncan so he can be king, as the witches prophesied.  However, even he understands that there is no reason to kill Duncan.  In a soliloquy, he says that Duncan has done nothing to deserve death.

He's here in double trust;
First, as I am his kinsman and his subject,
Strong both against the deed; then, as his host,
Who should against his murderer shut the door,
Not bear the knife myself. (Act 1, Scene 7)

Lady Macbeth talks him into it.  She is convinced that they will not fail, and she goads him into action by telling him he is a coward.  He does not seem to be able to stand up to her.  She convinces him not that the action is right, but that they will get away with it.

After killing Duncan, Macbeth is a mess.  He is already starting to hallucinate, because he is guilt-ridden over what he has done.  When he was in the room with Duncan and the guards, he thought he heard them calling him a murderer.

Methought I heard a voice cry 'Sleep no more!
Macbeth does murder sleep,' the innocent sleep,
Sleep that knits up the ravell'd sleeve of care,
The death of each day's life, sore labour's bath,
Balm of hurt minds, great nature's second course,
Chief nourisher in life's feast,--  (Act 2, Scene 2)

Lady Macbeth tells him he has nothing to worry about.  She does chide him for not leaving the daggers with the bodies.  That was part of their plan for framing the guards and Duncan’s sons.  However, Macbeth was too upset to go back into the room and face what he had done.  His guilt only grows from here, along with the death count.