> Why are people so eager to gatekeep who gets to call others mentally ill?
Because calling someone mentally ill is a serious thing to do, and doing so without being qualified to offer that diagnosis is irresponsible and cruel.
> I don't have to be a doctor to say that someone who is constantly coughing and having a fever is sick, nor do I have to be a doctor to call someone with no legs disabled. What's different about mental illness?
If you can't understand the obvious, huge difference between those things, then I'm not sure what to tell you.
Because calling someone mentally ill is a serious thing to do, and doing so without being qualified to offer that diagnosis is irresponsible and cruel.
> I don't have to be a doctor to say that someone who is constantly coughing and having a fever is sick, nor do I have to be a doctor to call someone with no legs disabled. What's different about mental illness?
If you can't understand the obvious, huge difference between those things, then I'm not sure what to tell you.