These things make ST great. Star Wars is too realistic. An Imperial Officer messes up just once he gets Force strangled to death. No Imperial Officer has EVER said anything along the lines of "to hell with their orders", he is to worried about carrying out every single order to 100% perfection to avoid sudden death to be considering the possibility of thinking about maybe even letting the idea of insurrection or even "skipping a step" of any given order cross his mind.
One wonders in what military the summary strangulation of officers is considered "realistic," but I'll let that pass.
It is an exaggeration to say that if an Imperial officers messes up once, he gets strangled. We have seen very few Imperial officials strangle members of the Imperial Armed Forces. The chief offender is probably Vader; others may exist, but I cannot recall them. Vader's wrath may have been legendary, but he was still only one person, and there were billions in the Imperial Armed Forces. Most Imperial officers, especially those below flag and general rank, could safely trust that they would never meet Vader. They would not be motivated by fear of Vader, any more than a modern officer of the United States is afraid of Robert Gates writing him a bad OER.
We should also not assume that the all Imperial officials were as intemperate as Vader--or that they all enjoyed his protection from prosecution. Vader was the Emperor's pet, known to the galaxy as the last loyal Jedi and to the elite as the Emperor's Sith protege. He was effectively immune to retaliation from those he wronged. Most other Imperial officials would not have this protection--they would be subject to Imperial law which, we suspect, proscribes the summary execution officers, or at least limits that power to the very highest echelons of power. Bound by law and the threat of vengeance, other officials would temper their behavior and simply not commit murder when a court martial and death sentence would do.
The Star Wars films portray a tiny segment of the Imperial Armed Forces, that which interacts with Darth Vader, and that segment should not be considered entirely representative of the whole.