Mainstream culture has become exceptionally literal; we now have a hard time processing tragedy or satire. The recent 40K controversy illustrates this neatly. If I was Iain McGilchrist I might attribute this to the creeping dominance of left-brain thinking, but sometimes I wonder if the problem is just that people aren't spending enough time reading proper books.
How does one define tragedy? I think the simplest and best description is that tragedy is fiction which reminds us that fundamentally virtuous people with good intentions can nonetheless end up in bad situations (and, perhaps, those bad situations arise precisely because of those good intentions).
How does one define satire? Again, sticking with a simple description, it is what Chesterton called the "only moral to everything": "[S]uperiority is always insolent...pride goes before a fall...and [there] is such a thing as being too clever by half." It is fiction that reminds us that people often puff themselves up with their own sense of virtue and thereby overlook the fact that they lack it in crucial respects.
Tragedy and satire are in that sense two halves of the same coin. They remind us that there is not a direct line going from having a sense of acting virtuously and achieving virtuous results. Basically, happy endings don't follow from being "a good person". The main difference is that in a tragedy, it is probably necessary that the protagonists are actually good people, whereas in a satire, they aren't, but think that they are (or present themselves as such).
It is foolish to suggest that tragedy and satire each only serve one function, but they undoubtedly share a main function, which is to remind us that you cannot immanentise the eschaton. You may think yourself to possess powerful insights that will allow you to realise a better world, perhaps even an ideal world, but you are undoubtedly wrong. Your vision will only realise itself as tragedy or as farce.
This is why political extremists of all stripes hate and fear both tragedy and satire. Soviet and Nazi art were nothing but kitsch: art in which "shit is denied". For the ideologue, there is a path from having the right intentions to the right results. There is no space for tragedy or satire in that kind of moral universe. Both tragedy and satire are fundamentally about shit - reminders of the existence of shit - and that cannot be tolerated. If one believes that one is on the path to achieving a desired end-state, then the inevitable continued existence of shit has to be denied, and forcefully.
Warhammer 40K embodies elements of both tragedy and satire. On the one hand, having good intentions (defending humanity against foes which would see it utterly corrupted or destroyed) does not necessarily lead to good outcomes, and in fact, ironically, itself creates bad ones (what you are defending itself becomes corrupted in the attempt). On the other, it has always had its tongue in its cheek: yes, the space marines look cool, but they are also ridiculous, melodramatic and po-faced, and we're all in on that joke. And, of course, if you don't want to think about it in either of those terms - look, John Blanche art and cool models and explosions.
In a literalising culture like the one which we inhabit, one wonders if this can last. Sooner or later, will the powers that be at Games Workshop be forced into playing down these elements of tragedy and satire, and transforming 40K into something more recognisable to mainstream understandings of the nature of fiction? Something more akin to the kind of morality play which increasingly dominates film, TV and fiction, in which the good people with good intentions achieve good results in the end and the bad people get their just deserts? At the moment, their defence against accusations of political incorrectness (yes, we have honestly come to the point at which a fictional dystopia which nobody in their right mind would want to live in, set 38,000 years in the future, is being criticised for being politically incorrect) is tipping into a reliance on it being a "satire". I don't expect that to last.