I'm not following you.
Do you mean what the attraction is TO the dark side of spirituality? What would draw people to it? Or, do you mean, what a soul that IS in the dark side, desires?
to the 1, I would say;
1 I would say the excitement of the unknown, or perhaps the temptation of having some sort of control over life, and it's ups and downs.
To the 2, I would say;
2 The desire to get away from it, to find something that satisfies the soul. Those who have been in darkness and have subsequently found the light, have testified of this.