Power gives one focus. The Dark Side gives power. Those who operate chiefly on the Dark Side are affected by power-lust, as power is addictive.
Thus, using the Dark Side powers doesn't make one evil, any more than someone who uses the Light Side powers makes someone good. What makes a person good or evil is the intent behind what they do: are they seeking personal gain, or are they doing what they do because it's the correct decision in the situation? Sometimes it can be both, but that's more the exception than the rule.
If your intent is selfless, you are generally considered good; if your intent is selfish, you are generally considered evil. When Bill Gates donates a billion dollars a year education and humanitarian relief, people don't stop calling him selfish or evil... I mean, really: is it just a PR trick to try to be a better person than the money-hungry monopoly he helped to create, or is he really trying to do good things with his money?
The issue is always one of intent, not of the tools used. But if one uses only the tools of the Dark Side, then their aims may be corrupted. It's difficult to tell what the aims are without long-standing looks at the way that people behave. If their aims are generally benevolent, then their results will show it. To this end, these people can be said to be \"good people\".
But the Dark Side of the Force is indeed seductive. It is attractive, mysterious, and alluring. It is easy. It is simple. And in addition, it is destructive. These all have their place in the grand scheme of things, but they can be easily misused for evil purposes... and when only these tactics are used, then a person can be said to be an \"evil person\".
Both of these are judgment calls. Both of these are valid ways to accomplish one's goals. But great care must be taken, because the Dark Side's allure and temptation are greater than the Light Side's, because the Light Side tends to be unpleasant where certain things are concerned.
This is also where attachment comes in. Attachment is dangerous, because it causes us to be able to have our actions forced by other people. We cannot be simultaneously in control of ourselves and out of control. But we can be in control of ourselves and under the direction of other people. But again, our attachment to things and people--our greed for recognition and ownership--is the primary means of our undoing.
I stand by what I believe (just as I'm sure that others are standing by what they believe). The issue with trying to define what is 'Light' versus what is 'Dark' is a matter of judgment and discernment. But in general, things which are creative and life-promoting are 'Light' because they help us survive (and as every Darwinist knows, those who have a focus on survival tend to be better survivors, and so because of this we have more people with this ethic than not); while things which are destructive and which serve to detract from survival are 'Dark' because they promote only the survival of the individual at the cost of the rest of the species (again with the Darwinism).
I can come up with fancy explanations until I'm blue from lack of breath, but the result is the same: either I convince you, or I don't. And if I don't, then very little is likely to do so. Yet I debate because my experience with the ethic I've chosen has worked to explain a great many things which I wouldn't be able to understand differently.
