I personally prefer to inform the officer of firearms in the car as my pistols are often sitting on the passenger seat. And I would rather he know about them and be informed of my cpl than him discovering them and pulling his sidearm out in alarm. I would like the officers mind to be at ease and make his job easier. Their jobs can be stressful enough. If I can put his mind at ease then he will likely go easier on me.
Do you extend the same courtesy to the convenience store clerk when you enter their store? They have no idea if you are a criminal coming through the door intent on robbing them by shoving a gun in their face or looking for a cup of coffee to keep you awake on a long drive.
Do you extend the same courtesy to the cab driver if you happen to be in need of a cab? They have no idea if you are a criminal getting into their cab with the intent of shoving a gun in the back of their head and demanding any cash/credit cards they might have or if you are just wanting a ride home from the bar because you had too much to drink.
Or are police officers just a special class of citizen that deserve to be "at ease" more than other human beings in other occupations that are more likely than others to be victims of violent crime?