The Empire is a gun, the Sith are guys point and pulling the trigger. The gun has no say, while it may not be directly evil, it is an evil thing by proxy as it is being used for an evil purpose.
So putting armour piercing bullets in the gun (helping the Empire), is always a bad thing.
So trying to make that "gun" into something more than just a weapon is bad? Honestly believing that Imperial way of life brings prosperity?
Pretty sure it does make them "good guys".