@sonicfan  
Even if he has protective scales, its not going to protect him being affected mentally.  
Like the fact his own friends tossed him infront of a monster and such.  
Along with it will still hurt anyway if that thing managed to connect its attacks on him.

Commander Shepard did it too
 

Twilight is stupid, no wonder she’s an earth pony in G5.

Yeah, because you know dragon scales has the durability of wet tissue paper. /sarcasm
 
While it probably is pretty mean that Twilight would use Spike as bait, she was probably counting on his natural protections to keep him from being harmed, whereas most of those present didn’t have the protection which Spike does. Plus, it was during a moment of panic and stress, both of which Twilight has been shown to handle very poorly. While it doesn’t excuse her using him as bait, it does illustrate how decisions made in the heat of the moment may/can have consequences, unexpected or otherwise after the crisis has ended.

atleast your not eaten like most bait

At least she does not use him to monsterbate.