No it doesn't; he didn't say most individuals with psychiatric disorders are violent. He said they are more violent than people with non-psychiatric disorders, which the article supports (especially if they also have a substance abuse problem).
First, no, that is not true. Second, no one is trying to prove causation here, so it is irrelevant. Third, the existence of more violence is enough to justify avoidance, so causes and correlations can be left to policy makers and sociologists.
