Pretend you're a ref for a minute...why in the hell do you care if a coach will get mad at you? Why would it change when you blow your whistle? I can't tell if your contention is that referees get some sort of enjoyment out of making bad calls and would do so all the time if coaches didn't get angry...is that it? You think these guys all huddle up before a game and say "you know what, that Hoiberg is just too damned nice, let's realllly **** him over this game!", high-five each other, and then conspire to make bad calls? Or are you trying to say that refs don't call fouls that they should because they're afraid to get an earful from the coach? That's equally stupid, because A) they're not children, and B) they can always eject a coach if they're legitimately afraid of him.
There are certainly reasons for bad officiating, ranging from incompetence/inexperience to more nefarious things like betting...but grown men being afraid of getting yelled at by a coach is not one of them.