Can you? Look, the crux of mental illness is that the organ you use to understand the world and comprehend situations and consequences is broken. If I'm mentally ill, you can't convince me that I'm wrong or that I'm ill anymore than someone with liver disease can process alcohol. That organ doesn't do the job correctly anymore. Logic doesn't apply anymore.
How can you respect my autonomy if I'm wrong about my own safety? If I say "I don't believe the cold can harm me, because I believe there is a fire inside me", your choices are to respect my autonomy and find me dead tomorrow morning after the blizzard, or to not respect my autonomy and I'll be alive tomorrow. Bring an army of caseworkers to tell me I'm wrong- it won't matter. They can all watch me die too.
Edit: to be clear, I'm talking about the most extreme forms of mental illness, the absolute limit. Like a good unit test, always check the extreme examples to see if your solution works.