I think mentally ill people can also be evil. The two aren’t mutually exclusive. Most mentally ill people aren’t murderers. Even with paranoid delusions, many schizoid/schizophrenic people know right from wrong. I would say that Williams is not only mentally ill, but evil.
So schizoid isn't a mental illness, per se (at least not a severe mental illness). It's a personality disorder. It's called Schizoid Personality Disorder and these people are not psychotic. They avoid people because they like being alone, but they are fully functional individuals. They have problems with trusting others that can look like paranoia, but they are not the type who think the government is bugging their phones. It's a different thing than schizophrenia (as is schizotypal which is also a personality disorder).