I think a person becomes a lightworker as a natural progression of their awareness. As awareness develops, you experience first-hand that we are one. I know that sounds trite, but trite is also true in this case.
These experiences can build gradually, or in the case of what in Zen circles is called Kensho, they can come suddenly and powerfully.
However they arrive, after a while, people who experience life in this way, can't help but feel what others feel, and care about others the same as they would about themselves. To them there is no difference.
So, being a lightworker in that sense is really not a choice, as much as it is a result of other choices which may have been more, shall we say selfish.
Selfishness is sometimes the power behind self exploration. In that way, perhaps instead of being a polar opposite, the darkworker phase may be a step toward being a lightworker -- for some. Others may not be able to move beyond that phase.
Food for thought thought? What do you think?
John
Self Help for Sensitive Souls — Zen-Moments