If you could look into the hearts of a normal person vs. a person with a mental illness, I think that you would see pretty much the same thing. Mentally ill people are often quick to express their nastiness. But you will find nasty thoughts and feelings in the hearts of normal people too. We don't behave better because our hearts are better. We behave better simply because our self-control is better. Our hearts are just as bad. That's what Romans chapter 2 is all about.
When someone was on a rant (consider yourself lucky if it goes no farther than that!), I felt superior because I was able to stay calm and say nothing. But Holy Spirit zapped me about my thoughts.
"Her sarcasm is nasty!"
Sarcasm is always out of place.
"I'm glad that I don't speak like that."
You don't say it. But you think it! It ALL needs to come out !!!
Menatlly ill people have dirty hearts and express it. Normal people have dirty hearts and suppress it. But in God's eyes, neither is acceptable. He is not looking for outward behavior modification. He is looking for clean hearts that are free from negative thoughts and emotions.