Although I do not agree with Steve about many things he thinks/writes about darkworker, I think I fit into his definition.
I do not believe in a higher purpose (karma, God, devil, ying and yang, sin, redemption, good and bad/evil as moral categories, whatever) and therefore I do not believe that there is an absolute "good" that is to be attained by good works. Good is what pleases me and does me good.
So I see absolutely no reason to do things that benefit others, but usually I see no need to tell that to the people I am dealing with on a day-to-day basis.
Although I have to add that imho, even the "lightworker" as defined here is selfish to a certain degree: He gets personal satisfaction put of doing "good".