All their rules and such aside, a lot of people don't like the Grey Knights in their current incarnation because they see them as too... well, everything. Too perfect. Too white knight-y. Too knowledgeable about all the big secrets, too powerful within the Imperium's structure, too implausible even within the bounds of the fiction, and just too damn awesome.
Today, I'm going to give you another way to look at them, one that presents a very different story. Is it necessarily right? Of course not, there are hundreds of ways to interpret the fluff and GW has as much as said that none of them are any more "right" than any other. But it does give a whole new take on a lot of what the book says about the Grey Knights.
I don't doubt most of you are entirely aware of Grey Knights and are at least passingly familiar with their fluff. They punch daemons super, super hard and they're very secretive about it; neither of these changed from the previous codex, but the way in which they were presented certainly did. As written by Matt Ward, the Grey Knights are lauded as "incorruptible" defenders of humanity, able to not only fight denizens of the warp without becoming tainted but also wield rare and forbidden sorceries and even conjure, bind, or control daemonic entities themselves, all without risk of falling to Chaos's taint.
Moreover, they are zealous prosecutors of their duty to defend mankind- no obstacle is allowed to stand in their way. Should their duty require them to murder civilians for the greater good, so be it, and often this is the least of the sacrifices that they will make. Whole Imperial Guard regiments or planets have been wiped out to contain an infestation; even Space Marines are not above their measures, though they more commonly take their memories than their lives. It is made clear, time and time again, that the Grey Knights will do anything within their power- and their is little beyond their power, connected to the most authoritative organizations in the Imperium as they are- to ensure that no daemon escapes their grasp.
This straight read of the text is the basis of the common interpretation of Grey Knights as Mary-Sues of the highest order. They are the elitest of the elite, outranking by an order of magnitude even genecrafted supermen of other Space Marine chapters. Where even such titans might hesitate, however briefly, they stride forward with purpose and knowledge. Nothing is unknown to them; there is nothing they cannot do. They are utterly, absolutely perfect, without any flaw or blemish- after all, what they do protects the Imperium from absolute ruin, and it's made clear many times that daemons very much do have the power to corrupt, enslave, and destroy on a scale that can threaten all of humanity.
From this perspective, the Grey Knights are the ultimate, unabashed one-up codex; anything you can do, they can do better. You have rare and precious Terminator armor? Every guy in their chapter wears Terminator armor. You have masterful psykers who wield elderitch energies? Yeah, even their chauffeurs can do that. Your leaders bear the relic-weapons of an age long gone, unreplicable in these barbaric times? They hand those out to trainees on the first day.
However, as I have alluded, there is another way to interpret things. Students of culture may be familiar with the concept of hubris, the heroic flaw of overconfidence. Its use is especially common in the old Greek works, where many a brave adventurer was brought low by his own pride in his abilities. Hubris, then, is the essential flaw of great heroes- it basically represents you being too awesome, to the point where you destroy yourself.
Looked at through this other lens, we can get a very different sort of idea of the Grey Knights. Remember: every codex is written more or less from the point of view of its own faction, so it is only natural that the Grey Knights book touts them as being perfect heroes- this is, after all, what they want to be and see themselves as. But if we consider such statements with the aforementioned perspectives in mind, we have to begin to question them- the Grey Knights can't be literally uncorruptible, because if they were there would be no need to take any kind of measures to protect themselves. In fact, we can't even say that they are effectively incorruptible, as several times in the course of the book it talks about them taking additional steps to ward themselves against daemonic influence (we'll talk about one of the more controversial a bit later) and ascribes differing members of their order (Purifiers, Crowe, Draigo) above-normal resistance to the influences of the warp, which again implies that lesser members CAN be influenced by it.
So maybe Grey Knights aren't quite so "incorruptible" after all. But isn't it said- and been said in the fluff for some time- that no Grey Knight has ever fallen to Chaos? Sure, but the fluff says a lot of things. Is that a literal truth or the truth as portrayed by the Grey Knights to their own number? Certainly, if one ever did fall, it's unlikely they'd just let the information out- the Imperium tends to be close-mouthed at the best of times and the Grey Knights are absolutely paranoiac about the dissemination of information. If one of them ever fell to Chaos's influence, you can bet that he and everyone who looked like him would get the SHIT purged right out of them and any planet they had ever set foot on condemned to exterminatus.
Moreover, those of you familiar with real-world politics of course recognize the parallels between the Imperium's order and various autocratic systems of government, especially some of the crueler breeds of fascism, theocracy, and communism. Such governments almost always employ extreme means to achieve their ends, especially the control of information to their peoples, and in this regard the Grey Knights could easily be looked on as a "secret police" of the Imperium. While such organizations often hold themselves in the highest regard, fanatically shouting their devotion to the system they uphold, outsiders rarely share this respect, as it is inevitably the outsiders who are forced to make the lion's share of the sacrifices that are continually demanded "to prevent the destruction of our glorious nation," "for the betterment of all mankind," "to provide for His will," etcetera. So, while the Grey Knights themselves may be convinced of their absolute righteousness, it is more than safe to assume that many others would not necessarily hold that same opinion of them, at least if they knew enough about the Grey Knights to understand what was occurring.
So a picture begins to come together: an order of "holy" knights on an eternal crusade against an unbeatable enemy, ever demanding greater and greater sacrifices from those they nominally protect, supposedly immune to the evil they fight against but demonstrably not so. Can we see where this is going? We know that the Grey Knights can be corrupted, though they seem to be resistant to it. However, the powers of Chaos often work subtly and slowly, encroaching into their target by there merest fractions over long periods of time. Is it possible that, rather than being masters of the warp powers they claim to control, like so many other sorcerers they have instead become masters by those very same forces? What if the Grey Knights are the Chaos Gods' greatest joke on the Imperium, its "noble defenders" already taken- albeit quietly and in small ways, as yet- to the side of the enemy they fight? What does the warp care if Daemonettes or Beasts of Nurgle are discorporated and the Grey Knights claim a victory? The Immaterium is an infinite sea of such creations- slay one and another will rise in its place.
This would fit with our hubris theory- it would be, indeed, the Grey Knights very boasts of incorruptibility and perfection that lend it evidence. Convinced of their own righteousness, they would thus be free to explore all of the forbidden ways of sorcery- and 40K lore abounds with magicians who believed themselves untouchable by Chaos's changes until it was far, far too late. Such an interpretation also meshes more closely with many of the aspects of 40K's tone and theme than might otherwise be true- if the Grey Knights are perfect, they stand at stark contrast to shades of grey that virtually every other 40K army is portrayed in, but under this theory those same shades are returned to them; indeed, it reiterates that maxim of 40K lore that there ARE no real "good guys." In this context, their bloody massacres to keep their existence secret are more likely to be somewhere between rationalizations to sate a need they do not acknowledge and the erasure of evidence, consciously or not, for what they are.
But, of course, this is only one way to interpret the text of the book, an interesting mental exercise. Did Matt Ward intend for it to be read this way? Probably not; whatever I think of him as a rules writer, my conception of him as a fluff writer nowhere includes the words "subtle" or "nuanced." But taking the gospel of Games Workshop's lore and interpreting it in new ways is part of the fun of the hobby, and with that in mind I think it's a great way to bring additional depth to the army, especially if one is making unusual choices (Daemonhosts alongside Grey Knights, for example) or when allying in team fights.
(An aside on the story of the Blood Tide: read with the above understanding, of course, the narrative makes perfect sense, but even ignoring my little conspiracy theory, I think far too many people have taken the story to be many things it is not. Yes, the Sisters of Battle are basically used as punching bags to show how awesome the Grey Knights are- this is hardly unusual, as nearly every 40K codex does this with other races. Moreover the SoB are not uniquely singled out for such treatment- Imperial forces of all stripes are, in the course of the GK book, annihilated wholesale with only limited pretexts. The killing of an order of Sisters- unlikely to be more than a few tens of thousands strong at the very upper limit- is a drop in an utterly merciless bucket compared to the other atrocities that the Grey Knights commit. As to the matter of why the "uncorruptable" Grey Knights found need to slaughter them in order to make charms of purity, even taking the rest of my arguments in earlier paragraphs for pure speculation I think it is clear implicitly, if not explicitly, from the GK book that they are not incorruptible, merely very resistant, and to varying degrees for different members. So, then, which do you think the Grey Knights would hold in higher esteem: the lives of some holy martyrs, or their own reputation of infallibility? Especially given they would almost certainly have purged the planet following the action anyways. In that sense their murder of the order was pre-emptive, but that is all- the moment the daemonic incursion started the lives of every person nearby were already forfeit.
This is to say nothing of the quality of the story or Matt Ward's skill as a storyteller- I have quite limited regards for either. Nor is it to say that the story is particularly empowering, since the narratives of 40K are practically devoid of heroic and successful female characters despite nominal gender equality in most forces. I only argue that the story is not self-contradictory nor inherently misogynistic, as many have made rather loud and repeated claims.)
