Snape stared coldly down The Nose at Burke. "Spare me," he hissed in tones dripping icicles of contempt. "You were far from helpless. Yet even with all the death-dealing abilities at your command, you still expected to sit back and let others to do your fighting for you?" He barked a laugh like spitting a mouthful of acid. "Get over yourself, you pompous little coward.
What do you think would have happened to any noncombatants - yourself included - if we'd been fools enough to halve our forces and let them win? Oh, don't kid yourself, your aptitude with the Dark Arts wouldn't have saved you; worse, it would have piqued Riddle's greed. He would have ripped your mind apart and devoured your every last original thought. You'd be lucky if you had enough wits left afterward to beg for death.
Since you were evidently too self-absorbed to notice, we were at war, a war we had exactly one chance to win. That's why we did everything we could to ensure that everyone wasn't helpless, or did you think all that Defense training was just a random pastime?
What we did was our only chance. For your information, the shields were failing, inevitably. If we'd let them come down on Riddle's schedule, they would have fallen on the full moon; and given the superior numbers of werewolves in his forces, wouldn't that have been fun?"