Even back in the 1980s it was common knowledge that other than some leadership issues, the Empire were the good guys.
Look at the Ewoks for example. A primitive tribal people. And yet the Empire was able to build a massive shield generator and landing pad right next to their village without disturbing them.
The landing pad was built on pylons and the power generator was underground, so that there was hardly any disturbance to the forest. The Empire used a mix of walking and hovering vehicles, so that they didn’t even need to carve roads into the forest. Only the shield antenna poked above the tree-tops. The Empire was as “green” as they could possibly be. Small wonder the Ewoks had no real fear of them.
Along come the rebels, and what’s the first thing they do? They take advantage of the Ewok’s religion to convince them that their golden robot is actually a god, and by extension, that the rebels are the god’s representatives. Then they tell the Ewoks stories of good and evil, with the Rebels being good, and the Empire evil.
In short, they convince the Ewoks - who have club and spear technology - to attack the Empire with its blaster and walking tank technology. Many are killed. This makes even the Emperor look like one of the good guys.
Then the Rebels blow up the power plant and shield generator - near the Ewok village - with a nuclear-level explosion.
Then they blow up a Death Star - the size of a small moon - in low orbit around the Ewok’s planet. They stayed to party that night, but no doubt they left before the atmosphere and surface of the planet were laid waste over the following weeks by hundreds of cubic kilometers of metal wreckage raining down from above.
The Rebels were just evil.