So in the last post, I talked about the many objectively bad things the Illidari have done. A fair amount of that post was how they differed from the Knights of the Ebon Blade - the organization for the other hero (I say villain) class.
The Death Knights are a little different. In their bad days, there was no "ends justify the means" kind of rationalization of what they were doing, because their ends were literally the end of all life on the planet, converting everyone into undead under the domination of the Lich King. And their switch from villains to heroes was a very conscious choice at a key moment.
The motivations for this change are actually, I think, a bit open to interpretation. I've always been under the impression that the power of Light's Hope Chapel (the many righteous dead buried there, whose tombs you can now visit if you're a Paladin) broke the connection the Lich King had with the Death Knights' wills - a bit like how Illidan cracking the Frozen Throne allowed the Forsaken to break away.
But there's another element to it, which is that the Lich King used the Death Knights as fodder - he didn't expect them to survive the battle. The key was to draw out Tirion Fordring and hopefully kill him before he could lead the effort against the Scourge in Northrend.
After this point, the Ebon Blade made the Scourge target number one.
Death Knights, by their nature, have disturbing methods. But if we are to judge by Thassarian's example (who granted, is kind of the moral paragon of the Ebon Blade,) the Death Knights are now basically the same people they used to be, only now with a consuming addiction to causing pain.
Thankfully for the Death Knights, Azeroth is a world that is constantly beset by demons and elementals and aberrations who can be fought without remorse. And so for the past few expansions, Death Knights have more or less blended in with the rest of the Alliance and Horde forces.
In Legion, though, thanks to the fact that there are actually class-specific stories again, the Ebon Blade has been up to some really shady stuff.
The 7.0 class hall campaign for Death Knights has you assemble a new Four Horsemen to serve as champions for the Ebon Blade.
First off: the reason you're doing this is because the Lich King told you to. While it's Bolvar, and not Arthas, who you're dealing with, it has become very clear that the Lich King itself is the real dominant personality regardless of who is wearing the crown. Bolvar isn't trying to sweep over the entire planet with undeath, but he's definitely not turning Icecrown into a friendly ski resort town either. There's a definite question of whether the Lich King is truly trying to keep the undead under control or if the Scourge will arise as a threat once more in the future. And if that happens, it has become surprisingly unclear what side the Ebon Blade will be on.
While raising anyone as a death knight without their prior consent (so, basically all death knights except I guess Baron Rivendare?) is of course horrifyingly immoral, the campaign ends with the most brazen and villainous thing any of the classes do during their campaigns.
Seeking the fourth horseman, the Lich King sends you to retrieve the body of Tirion Fordring. Not only would turning this great paragon of the Light who very specifically fought against the Scourge into a Death Knight be a cruel fate to impose on one of Azeroth's greatest heroes, doing so also requires you to attack another order's class hall.
It's also a pretty terrible plan, given how the last attack on Light's Hope Chapel went for the Ebon Blade, but that's neither here nor there.
Death Knights fight their way into the Sanctum of Light, slaying paladins who are guarding the order hall. Ultimately, as they attempt to get to Fordring's resting place, Lady Liadrin shows up and lays the smackdown on them, leaving Darion Mograine dead. However, for a Death Knight that's more of an inconvenience, and he is raised in Tirion's place to lead the horsemen, taking on the role that his father had way back in the original Naxxramas raid.
As of yet, the Ebon Blade has not had to pay any real price for attacking their allies.
But they're not even done.
Spoilers for something in 7.2, just to warn you:
Death Knights will be sent to Icecrown to raise an ancient dragon corpse, but in order to discover its true location, they have to go to the Ruby Sanctum and access their archives.
Now, a normal person would, you know, ask. And given their intentions, they'd lie about what they were going to do with this corpse. But rather than that, you actually go into the Sanctum and kill a bunch of red dragons (and remember, dragons are sterile after the Hour of Twilight, so you're basically killing members of an endangered species.)
After slaying Silver Hand paladins and red dragons, you really have to wonder when the Ebon Blade is going to pay a price for all of this. In fact, unlike pretty much all of the other class campaigns (I think it's them and Shamans,) you don't actually do anything to fight the Legion. If anything, the damage you've done has hindered the war effort.
Death Knights aren't going to be nice, sure, but one would think they couldn't go around doing stuff like this without some consequences.