If you talk to God, that’s called prayer. If God talks to you, that’s called MAGA:
Why exactly is Nancy Pelosi’s aspiring assassin “seriously mentally ill?” Because he suffers from what experts in psychology would consider delusional ideation about Nancy Pelosi? By that standard, tens of millions of Americans are mentally ill, and for the very same reason — for example, pretty much anybody who watches Fox News and fails to notice that it is right wing propaganda, as opposed to actual news.
Trumpism, fascism, fundamentalist religion: all these closely related belief systems are shot through with florid delusions. If their sincere adherents (put aside for the moment the cynics who pretend to hold these beliefs for political gain, a category that I imagine includes most prominent evangelical leaders and Republican politicians) are delusional — and they are — then you might as well say that society as a whole is mentally ill, given the ubiquity of such beliefs.
And of course you can say that, but at that point the concept of “mental illness” is drained of any explanatory significance. It’s just another way of saying people persist in holding false beliefs in the face of all actual evidence, which in turn is another way of saying that they’re people.