Should you be eligible for criminally insane when self inflicted?

The Herald reports:

A grieving mother says she is “utterly disgusted” that the man who killed her son has been found not guilty of his murder on the grounds of insanity.

“There’s no justice. Not in this country anyway,” Pauline Dixon said after a court appearance in High Court at Napier on Wednesday.

Her son Patrick Reweti, 49 was killed by Chalton Mason Lawson in the Hastings suburb of Flaxmere on March 26, 2024. …

The court was told that at the time he killed Reweti, Lawson was psychotic, suffering from hallucinations and hearing voices, brought on by long-term methamphetamine use. 

He was using the drug every day.

I think most people would agree that someone who is insane due to factors they have no control over, such as schizophrenia should not be found guilty as they had no control over their actions.

But when your insanity comes from psychosis due to repeated drug use, I see that as somewhat different. It is well known that meth causes psychosis. If he had not started using meth, his victim would be alive.