The fact is, no care or conservatism whatsoever is warranted with such statements. A psychiatric diagnosis is no more objective than any arbitrary epithet. Anyone and everyone is free to call anyone and everyone else these names.
It's true that the clinical expertise of a psychiatrist or mental health professional is necessary to diagnose, only if by "diagnose" one means "get paid by an insurance company or the government for." Newspapers and media commentators presumably are not hoping to get paid as clinicians, so it's highly amusing that they are so self conscious about their statements.
Loughner killed and maimed a bunch of people, including a nine-year-old girl he'd never seen before. Of course he's a crazy, sick sonofabitch.
But nobody says any more than that when they pronounce him mentally ill.
Correctly "diagnosing" Loughner obviously won't help any of his victims in the slightest way. It won't help him either, he'll spend the rest of his life in unpleasant circumstances and it'll end badly. It might briefly comfort people who are terrified to see any real evil in the world and prefer to hope no one's responsible for anything, it's all just fate or the gods or neurochemistry. But in the long run, they'll all remain equally helpless against what we're experiencing as random violence.
So who cares about flippancy? Say Loughner's mentally ill, schizophrenic, anything you want. Just don't believe it should have anything to do with public policy. There's no viable anti-violence strategy in the field of mental health. There's no security in widely-available psychiatric evaluation and treatment. These "experts" don't know evil from a hole in the ground. Their drugs cause violence at least as often as they disable perpetrators.
The only "benefit" from all this care and thought that's going into whether or not Loughner is mentally ill, or how to tell, or how to diagnose others before they're dangerous, is money into the pockets of a special priestly class: guys who started out in the last century as, and who basically remain, users, frauds, charlatans.