harry potter - Why did Snape love dark Magic so much?

In her answer to another question, Slytherincess mentioned this from a chat with JK Rowling :

From a web chat:

Jaclyn: Did Lily ever have feelings back for Snape?

J.K. Rowling: Yes. She might even have grown to love him romantically (she certainly loved him as a friend) if he had not loved Dark Magic so much, and been drawn to such loathesome people and acts.

SOURCE: http://www.the-leaky-cauldron.org/2007/7/30/j-k-rowling-web-chat-transcript ... :)

What is it that drew Snape so strongly to Dark Magic™ that JK says he loves it?

The other dark wizard's seem to have a fixation on power, and merely use Dark Magic as a means to an end. Even their favouring purebloods is, in part a play for power over the 'less powerful' mudbloods.

So why is/was Snape in love with Dark Magic?

Answer

JK Rowling has gone some way towards addressing this in an interview (emphasis mine):

Nithya: Lily detested mulciber,averyif snape really loved her,why didnt he sacrifice their company for her sake [sic]

J.K. Rowling: Well, that is Snape’s tragedy. Given his time over again he would not have become a Death Eater, but like many insecure, vulnerable people (like Wormtail) he craved membership of something big and powerful, something impressive.

J.K. Rowling: He wanted Lily and he wanted Mulciber too. He never really understood Lily’s aversion; he was so blinded by his attraction to the dark side he thought she would find him impressive if he became a real Death Eater.

That said, I think Snape's family history must have had at least some influence on his choice. He grew up with an abusive Muggle father and a witch mother, which presumably instilled a prejudice against Muggles in him from an early age. This is already visible in the way he interacted with Lily and Petunia as children (see HP and the Deathly Hallows, chapter 37: The Prince's Tale).

So it was natural that he should seek to spend time with others who had similar prejudices - namely, Death Eater types - and from there the step to Dark magic is but a small one.

See also these excellent answers.