Why does Dumbledore make Snape DADA teacher?

[potioncat]

No: HPFGUIDX 158419

ghost_silver_wolf wrote: 
> Though it does bring up the question, why did Dumbledore hire
> Quirrell, Lockhart and Lupin, knowing he was putting them at risk?


Potioncat:
Dumbledore has hired around 40 teachers for that post, not just the few 
we've seen. OK, we might guess it took him 2 or 3 to catch on there was 
a curse. We don't know how bad the events were for those who came 
before our time. 

You know, it was very, very risky to hire a werewolf when you know 
something bad is going to happen. I wonder if DD was hoping all along 
that Lupin would be outed in a major way so that he could go 
undercover. Still, it could have been much worse.