Snape's motives for joining the DE's was Rowling interview transcript

[pippin_999]

No: HPFGUIDX 180363

Irene:
> I still think that's a ridiculous motivation for Snape joining DE. It's 
> in the books that Lily chided him repeatedly for his choice of friends 
> with interest in Dark Arts. How is it possible that he thought becoming 
> really good in Dark Arts is going to impress Lily?
> 

Pippin:
Canon shows he didn't take her objections very seriously, just like
she didn't take it seriously when he suspected The Marauders of being
up to something worse than being toerags. He was attracted to power
and IMO he was young enough to  suppose that everyone else was too. 

He couldn't have the power of being rich and popular and pureblooded 
like James and Sirius, but he could have the power of dark magic and
a powerful master.

I'm sure Lily's revulsion was beyond him. I doubt he could
see why beating up on Mary for being Muggleborn was so much 
worse than beating up on Severus Snape because he exists. 

Pippin