How about you borrowed your expensive camera to a friend and you noticed he left it visible inside his car on the parking lot. A parking lot known for many burglaries, in other words he was inviting somebody to steel your camera.
Would it be ethical to check if he locked his car so you can protect YOUR OWN belongings?
I agree with your statement, but looking at my log-files I wonder why the good guys should not be allowed to perform one scan while the bad ones are performing hundreds a day. Why should the bad ones have all the information?