Evil by definition cannot exist without good, and vice versa, you can never have one without the other, just like light and dark.
As to your definition of the Empire - the exact same can be said regarding the Republic. It's all about how things are played out, gone about and realistically how the PR spin is put on them.
Don't delude yourself that the Republic is the shiny gold bastion of all that is squeaky goodness, people died to build the republic and many of them were slaves or even simple collateral damage that didn't agree with the views of the republic.
Both factions will do what it takes to get the job done, both sides have and use slaves. Both sides have shiny heroes and evil villains.
When you blow up a temple to strike fear into the populace is no different than blowing up a power station and depriving the citizens of living essentials; cutting off life support, shutting down medical hospitals, security domes, fences and the like - just to get the other side to surrender quicker, or enter negotiations with minimal casualties (note in both cases both will still have said casualties) - such is to happen in war (or just when you want to force a planet to join your empire/republic).
Altruism exists on both sides of the fence and destructive forces that can detonate planets killing billions in a single act exist on both sides, both sides will do what is needed to get done, there's just more goody-two-shoes trying to hide the past in the Republic.
Just because you are the victor from your conquest doesn't mean you are just, benevolent or even morally right in what you've done (tho you may believe you are).
In the end, Red=Dead and the Jedi will pay, the Republic supports, harbors and protects the enemy of the Sith, any of those that get in the way are simply collateral damage.
