SkunkyArt | Songue — Motivation

Actually, there is very strong evidence that Sasuke is actually clinically insane, at least in his obsession to kill everyone. There is a mental condition called delusional disorder, and looking at the symptoms, they seem to have been written about Sasuke. I'll post a copy of the list from The Other Wiki below:

The patient expresses an idea or belief with unusual persistence or force.

That idea appears to exert an undue influence on the patient's life, and the way of life is often altered to an inexplicable extent.

Despite his/her profound conviction, there is often a quality of secretiveness or suspicion when the patient is questioned about it.

The individual tends to be humorless and oversensitive, especially about the belief.

There is a quality of centrality: no matter how unlikely it is that these strange things are happening to him, the patient accepts them relatively unquestioningly.

An attempt to contradict the belief is likely to arouse an inappropriately strong emotional reaction, often with irritability and hostility.

The belief is, at the least, unlikely, and out of keeping with the patient's social, cultural and religious background.

The patient is emotionally over-invested in the idea and it overwhelms other elements of their psyche.

The delusion, if acted out, often leads to behaviors which are abnormal and/or out of character, although perhaps understandable in the light of the delusional beliefs.

Individuals who know the patient observe that the belief and behavior are uncharacteristic and alien.

Looking at this, as well as Sasuke's recent OOC moments, we can almost certainly diagnose him as having Delusional Disorder.