Do not tell aggressive psychiatric patients to calm down. It will not work. They may attempt to whack you upside the head, as my partner may or may not have discovered.
If they think they're perfectly fine, smile and nod and treat them like they're perfectly normal. Agree that they have every right to be perfectly upset about the situation. They want to bring a stack of bibles? That's fine, but advise them they might get lost in the ER. They want all six of their baseball caps? Sure. You'll even make sure they don't fall off. Let them rant. They think the doctors are out to get them? Reassure them you'll make sure the ER doctors are good.
This would also be how I got my patient to hand over his belt, shoes, and the aforementioned stack of bibles when we got him to the psychiatric holding room at the ER. For safekeeping, of course. Totally normal.
Because yes, paranoid schizophrenics do present a danger to the long term care facilities they reside in when they become agitated and aggressive.
But they have every right to not be reprimanded to control behavior that they literally can't control. At least for the ten minutes that they're in the back of my bus.
For all you know, on some deep level, they themselves might be terrified at what they've become. Imagine being trapped in a mind that you can't control.
They're still human. You just reason with them a little differently. And you may have to repeat yourself a few times, cause it won't sink in at first.