He'd just been attacked by a magical source that disarmed his weapons at the wrists, was cast wordlessly and without wand motions, and did not leave an obvious bolt to block. This is probably a bad time to show off.

At a deeper level, Voldemort (and Mad-Eye Moody) favor a combat philosophy of dodging, under the quite reasonable realization that there are a large number of spells that can overwhelm shields or are unblockable.

The Officials involved have believed Quirrel to be David Monroe for a long time (chapter 84), that seems to have become the Official Story over the last couple days, and Mad-Eye Moody knew that Quirrelmort should have been fired out of a cannon into a sun as soon as he took the Defense position, so they've been asking questions and taking the first reasonable answer for a while.

I'm fully expected Moody to dive through a door with stunners flying, yelling "Not paranoid enough!" because /someone/ didn't expect door transfiguration, but most of the other people involved have already gotten suspicious and had their suspicions allayed.

Then he'd be an eleven-year old surrounded by bleeding but live adult Death Eaters, and with only (and specifically) two tourniquets, with no easy way to get them medical attention or stun them.

There's ways to incapacitate them less lethally, but you'd need to think a little further outside of the box, and they're not really compatible with MoR!Harry's outlook nor the narrative progression.

We have strong evidence suggesting that bringing people back to life is possible in this setting, and turning wizards into the same person except not-magic is possible. It does not require God-like powers, or even as much investment as bringing them back to life as magical beings, so much as it requires MoR!Harry to have been more invested in his ethics.

Of course, if he were, then they'd probably not have needed to die in the first place.

On the other hand... According to various world clocks, 37 people die every 15 seconds. I'm not so heavily into the effective altruism movement as to make an enemy of all but the most efficient options, but it's a number to remember. Most alternative methods for incapacitating the Death Eaters less-lethally would have had greater risk of failure, and most methods for would require significantly more time and magical power than saving an average life.

For as much as it makes Harry sympathetic to wish he didn't kill them, there's only so much investment to that purpose before it would be bad thinking of its own -- even if you don't value their lives less.

In a search for kindness, not using cloistered information for personal advantage, and low tendency for factionalism, "child of a Death Eater" is a pretty hard constraint.

Quirrel had seen Harry use /Diffendo/ on some trees, and later that the trees have been cut. He was unconscious (and in an extradimensional bag) when Harry had cut through the wall in Azkaban, and only saw a cut circle of wall. He may not have known that Harry had anything up his sleeve more complicated than a Cutting Charm; he certainly had no reason to believe that Harry could wordlessly transfigure the tip of his wand into well over a hundred feet of braided carbon nanotubes. Quirrelmort has never seen -- only Dumbledore, Hermoine, and Professor McGonagall have.

But that's really not the part that got him.

Quirrelmort had accepted the risk that Harry could have escaped, or killed everyone present, just as he accepted the possibility that the Unbreakable Vow wouldn't have been enough to stop Harry from destroying the world. If he were absolutely certain, he'd not have bothered with backup plans. He did not care about the deaths of the present Death Eaters, and losing his own body was merely a minor setback. It's Harry's ability to instantly and permanently incapacitate without letting Quirrelmort's spirit loose that made the threat serious. That's a problem Dumbledore was relying on an ancient and frighteningly powerful artifact to implement, and Quirrelmort's mode of thinking doesn't exactly encourage thinking of these matters..

It's implied that more experienced wizards and witches can freely transfigure objects at a range, but Harry can't do that. However, even without Partial Transfiguration, objects that have been joined together can be transmuted as a whole (see chapter 28, with a wand touching one part of an object and converting parts into different components. We've also seen transfiguration operate differently on different components of a system. Once Harry has stuck spider-silk between his wand and a Death Eater, he can convert components of the Death Eater as easily as if he were standing next to them.

Harry's not shown any interest in this sort of biochemistry (the closest we've seen is a reference to "knockout gas", which means he knows less than nothing), and while propofol was well-known in 1992, it's not referenced in the sort of literature he's likely to read, he has been trained not to consider transmuting humans, his character isn't really aligned with less-lethal conversions, and there is a very high complexity penalty to this plan.

There are also some possible volumetric issues. We hadn't gotten an actual transfiguration rate since chapter 23, where he could only do five cubic centimeters per minute, while it would take about ~15 cubic centimeters of propofol to rapidly sedate this number of Death Eaters. The post-exam chapter gave an update of cubic millimeter "as fast as he can concentrate his will and magic" and "in a fraction of a second", which is imprecise enough to be useless. He was able to transfigure a unicorn in about an hour and a twelve-year-old's corpse fast enough to avoid notice, recently, and presuming unicorns are similar in volume to even a small horse he'd need to be moving much faster than 15 cubic centimeters a minute (900 cubic centimeters is less than a liter, a very small shetland pony would operate somewhere in the area of 180-200 liters, so... not sure folk did the math on that one).

But it's interesting as a thought experiment.

This isn't the only or even a particularly useful option -- Voldemort's gun could be rigged to fail in a cubic milimeter transfiguration, and to catastrophically fail in a cubic centimeter transfiguration; wands become dramatically less useful when they and their owner's fingertips are coated in a fine layer of teflon, vocal cords or the median nerve turned into cheese at about 1.5 cubic centimeters per person would make even wandless spell-casting impossible. More destructive but non-lethal options are left as an exercise for the reader.

What are you talking about here?

In Chapter 16, Quirrelmort instructed the class in a very simple hex that caused a small amount of pain and no lasting harm called Ma-Ha-Su. He then selects three students, Hermoine, Draco, and Harry Potter, and then requires them to select a student and fire Ma-Ha-Su at them, taking Quirrel and later House points for non-compliance. The comparisons to the Millgram Experiments become explicit in chapter 63. Hermoine refuses, Draco fires on Hermoine, and Harry fires on himself.

Harry explicitly beats Quirrelmort's plans, here : "Yes, quite ingenious, but there was a lesson to be taught and you dodged it." It's not clear he ever gets the intended lesson, given that Quirrelmort seemed to intend to teach Harry to harm Draco on obedient command.

Interestingly, this could have not just failed but have gone horribly wrong for Quirrelmort, and he wouldn't have even understood why. One of the common responses to Millgram-like actions in the last few years of science fiction is to turn on the person giving illegal orders. Harry wouldn't do that because of his upbringing, but other possible Riddle-clones would wanted to fire Ma-Ha-Su on Quirrelmort and claimed he counted as a student -- and either required he flinch or dodge from a trivial spell, or risked publicly triggering the resonance that would have brought Dumbledore down on Quirrelmort's head. The man's not exactly been known for his happy subservience, after all.

Even without reaching that unlikely but disastrous possibility, 'success' would have had dramatically different results than Quirrelmort expected, given Quirrelmort's difficulty understanding what Harry was trying to do with Draco even at that point. Blunt, blunt stupidity.

What does this mean?

Command Push is set of force philosophy where commanders give direct orders involving not only a mission's goal, but also its execution, tools, and specific tactics. It's very common historically, where communication is slow, or where the commander has much greater understanding of the field than individuals, but it's highly dependent on commander skill and knowledge, and very vulnerable to subterfuge. Quirrelmort is hugely prone to this, as are Harry Potter and (to a lesser extent) Draco.

This is usually contrasted with Recon Pull, Mission-type Tactics, or Command By Negation, where commanders provide goals, time constraints, and resources, but allow units to develop their own strategies to achieve those goals. This requires more training, faster communications technology, and higher levels of trust in subordinates (less so in Command By Negation, where you at least double-check with a commander), but puts more minds on a problem and can more readily adapt when lines of communication are cut or when situations on the ground change.

((Command Push and Recon Pull are video game terms from the Civilization series: different armies have different terms for these philosophies, usually subdivided into separate generations or divided by recent inspirations. Modern armies tend to use more modernized techniques derived from combinations of the two branches and further IT developments, though they'd not really be practicable in the time frame present here.))

Is that what we've seen presented so far?

Dumbledore won during the Battle of the Three Armies. His assault on Azkaban would have gotten him killed (and more seriously, set back his efforts by years) for a stupid communication error, were Harry not willing to risk his own life and invent new magic to save the man. Hermoine outlasted several hours of the Defense Professor's most aggressive psychological attacks possible, using fairly basic deontology. His 'lesson plan' with Ma-Ha-Su in Chapter 16 was bluntly stupid, even if Harry hadn't used the easy way out. In Chapter 35, he fears that Harry has screwed over his plans because of voicing an obvious disagreement that Harry has repeatedly given privately before.

And that's before we get to the stupidity that was enforced by canon : testing multiple novel spells (Horcruxes, however he 'reformated' the young Harry Potter) without sufficient and verified safeties, the highly fractious Death Eaters, the lackluster war with Dumbledore.

Quirrellmort is smart. He thinks ahead. But his fundamental philosophy is still very restricted. As much as he tries to claim otherwise, he's running on distilled Command Push -- we'll note that no Death Eater gave him advice in this chapter, nor would we expect them to. His speech in Chapter 34 follows the same philosophy.

But more importantly, he underestimates risks. He's a partially-formed rationalist, who has heard of Kolmogorov complexity but can't quite understand why he should shut-up-and-multiply yet. He leaves Harry a wand because wanded Harry is only a threat because of that wand if he has a) wordless, b) motionless, c) wanded, d) magic that can instantly disable Death Eaters, e) can hit him at all and f) threatens an immortal. It's understandable to not think Harry is a risk. A full-grown wizard in the same environment wouldn't be a risk -- Dumbledore or Mad-Eye Moody would have died, and died quickly. That's not as unreasonable a mistake as you'd expect.