Some people are too embarrassed or afraid to admit that they have mental illness. Even if they have diagnosis and many symptoms, they still lie deny it.

Then they project their own embarrassment and shame on other people and literally lash out at others with MI.

But there’s another issue at play. Many people refuse to get help (or can’t seek help etc) so instead they self medicate with alcohol and drugs.

Then their behavior is out of control but again they won’t seek treatment but instead lash out while intoxicated.

In my experience decent people don’t mistreat those with mental illness. The only ones who do are projecting because they are in denial or people with substance abuse issue and not seeking help with the issue.

Most people don’t get nasty unless they are drunk/high etc