Writing Jedi is fun simply because this type of question is allowed to exist in the mind of the writer. Are the Sith evil? Are the Jedi good? Write long enough and you'll be given plenty of opportunities to be challenged towards just such things. It makes the whole experience that much deeper.
Karen kills Blackguards and Gray Jedi all the time. It's what makes her so interesting to write. She wants to be a good little Jedi but just can't seem to see how keeping them alive and unrepentant is a good thing. She's seen the revolving door, she's seen the world's laid waste, and she knows that not all Force Users are created equal. That said, she still thinks death is a great tool to use for galactic education. Does that make her evil? Well, yeah. It just might. And she owns that and I as her writer own that. But I'm not going to give her a Sith Tag just because she makes mistakes and believes a little in her own flawed humanity.
Real world example: If the God of Israel himself says we are all sinners, I don't think that is prerequisite enough to make all of humanity worthy of being called Sith. I think you just call being fallible an example being a good human. Likewise, I don't think that being a sinner disqualifies you from being a Jedi. I think being a sinner is absolutely necessary to being a good Jedi. But's that's a moral that can be hard to understand.
So. Are the Sith Evil? Well no... I think the Dark Side is entropy and it's followers just tend to want to become Avatars of it. It's like, evil by association in a way. The struggle to become Pure Evil keeps them human in a way. Like every single Sith seems to understand that there is a righteousness housed deep within them that must be expunged or burned out. And I think a lot of Jedi Heroes notice that. I think the Jedi notice that the Sith feel a need to fight against good. Not just outside themselves. But inside themselves too. Meaning that even a Sith can recognize the potential for good within themselves. It is what defines them. The Dark Side does not call a Sith evil. It is the Jedi who must define the Sith.
This is what makes the Jedi Path so darn amazing to write. Because eventually you reach a level were all the Sith you've been fighting stop being evil, and start being a mirror image of your own potential for darkness. A weakness that you yourselves possess simply by being fallible. Suddenly all those Sith you've ever fought, killed, or were wounded by... Are just other lost souls. Like you. People who in different circumstances and with different choices, could be right where you are standing now. As a fighting, struggling, and emotional being. A real and working Jedi.
There is a peace that can come as a Jedi when you realize that all your enemies are not evil in-and-of themselves. Though they might strive magnificently to prove it. It reminds you relevantly that there is nothing to fear, but fear itself. Because your good. Deep down, we're all good. We all possess the spark to become good people. We just haven't realized it or tried hard enough to prove it yet. And that some people will spend their entire lives fighting against goodness just to prove to themselves, in vain, that they can never be like it.
Luke could always have lifted up that X-wing from the swamp. Yoda knew that. Luke Skywalker could always have been Luke Skywalker. He just needed to believe hard enough and live hard enough, to prove it to himself. And it was that love, that belief, that taught his father the same. Anakin Skywalker could always have been good Anakin Skywalker. The Clone Wars taught us that. He just needed to remember who he really was. Anakin Skywalker.
Star Wars is not about being good or evil. It's about recognizing the power and potential of the human heart. Us.