@blossom: At the risk of being self indulgent (hehe, who am I kidding, I love me), I made a post on the subject here.
And to elaborate: everyone needs to be selfish inasmuch as they need to care for their basic needs and act true to their own nature. However, when being true to yourself has you bend-the-knee before another and place your will secondary to his, you've officially stepped out of darkworker territory. The "he" in that last sentence could be a god, could be a man, or you could make it an "it" and substitute an ideal. No matter what, a lightworker is subservient to something else.
I like how Asmoday
put it: darkworkers expand their list of choices whereas lightworkers accept fewer and fewer choices. A darkworker needs to reason through their morality and decide on a case-by-case basis how they're going to act in regard to others whereas for lightworkers the most significant choice they can make is who or what they will serve. They will always retain some autonomy over their own lives if they choose well, but they are, as Asmoday stated somewhere else, "God with one hand tied behind their backs."
So to boil it down, it's the difference between self-determination and subservience. Both have their place, everyone is equally capable of either, but there are numerous benefits to picking one or the other (as Steve put it, expanding or contracting) for a period of time.