That's not a "what-if". I just read about a couple of dirt bags that were arrested for doing just that...dressing up like cops and breaking in. Anybody can buy a uniform/hat/badge/jacket and carry on.
That's why I say...whether you're a cop or a criminal (and it's getting hard to tell), if you break through my door, I will do my best to kill you, and you won't be bulletproof. I have nothing to hide, but I will not yield to the Blue Gestapo.