Then you are not a reponsible citizen. Attempted crimes are still crimes, and by preventing one, all you do is change the victim; the bad guy still needs money for drugs or whatever, so will keep trying until they get it. If you don't report attempted crimes to the Police, they can't remove the guy from society. You are fuelling crime with your actions, don't you see that? But this I think is telling. You are not confident that these people do actually have malicious intent, so don't report it to the Police, fearful that might identify you to the Police as the guy who has been complained about for flashing his gun around at normal citizens. If you were sure you were right, you'd have no reason not to report all of this stuff.