pizza delivery drivers and postal workers don't seem to have much of a problem interacting with dogs

False, they have problems all the time! And they are not in the same situation, they don't even go inside the house and act aggressively to the owners! People are happy to see the mail man and pizza guy and they stay outside and keep their hands to themselves.
I had a police officer pull over when I was walking my dog one time and I thought they were going to hassle me for no leash but instead she just wanted to say how beautiful she was and then she went on her way.

Of course if you google "cop shoots dog" you will get only stories of cops shooting dogs and then perhaps conclude that cops all live to shoot dogs, or you could google "cop saves dog" and then conclude that we don't even need the humane society!