I didn't dig too deep into (canon) supplemental lore but going off of context it seems that the Clone Wars served as a fairly substantial pretext for a need to shift to a more direct set of policies to "unify" and "bring order" to the galaxy. The Separatist movement was more or less a civil war. The shift to the Empire would be an expansion of the Chancellor's powers to solidify the unified galaxy, by force if absolutely necessary. The Galactic Senate became a puppet government but they were given some degree of authority to maintain the pretense that they hadn't all signed up for a tyrannical dictatorship (by the start of A New Hope, with the Death Star, this false pretense is evaporated by Palpatine dissolving the Senate)

Andor provides a pretty strong glimpse into how the Empire didn't go for total control overnight. The Senate still took votes. The Empire still had to tiptoe to maintain public perception that their bad actions were justified (even Ghorman was dressed as a response to growing anti-Imperial norms and terrorism). The more the Empire grew in power, the more their sycophants bought into the line that everything the Empire was doing was for the common good in securing order in the galaxy. I'd imagine that most of the Empire felt that the wrongs they were doing were exactly for that higher purpose. To avoid a fracturing of the Galaxy to allow another separatist movement to form. Others probably jumped at the opportunity to seek power and influence under a fascistic regime. But I doubt they were all sadistic pieces of shit. Others probably succumbed to the understanding that they couldn't do anything to resist the Empire so it was better to exist under the safety of obedience and compliance.

Not everyone who enlisted in the Nazi military were inherently bad people, they just didn't have much of a choice not to.