I think there has to be a nexus between the mental disorder and the offence. If someone has a mental disorder that is difficult to deal with but has nothing to do with the offence, they shouldn't get a lower sentence. They should only get a lower sentence if the mental disorder they were suffering from somehow contributed to the offence or prevented them from being able to avoid committing the offence. That's where there has to be a nexus.
On May 1st, 2018. See this statement in context.