But like I said, not all Slytherins are 'in the company of Draco'. There are six other year's worth of Slytherins who may or may not think Draco's the coolest since sliced bread. And if they truly wanted to join and learn DADA (especially if they needed an escape from pressuring parents/relatives), then who are the Trio or anyone else for that matter to say no? Even AD tried to get Draco to turn at the very end of HBP. So even the worst of the worst, so to speak, may want some place to turn to whenever they get in over their heads.

~Samantha Cate//Ravenclaw