The mortal world had a complicated relationship with Hell.
This is hardly a controversial statement, and probably requires elaboration.
The Circles of Hell were a known phenomenon, and their reputation as a place of suffering for deserving mortal souls was indeed a well-earned one; torture and slavery weren't at all out of the question, and more often than not an infernal city-state would function on a brutal system of meritocracy where the slightest gaff could result in a high-ranking demon either being humiliated and stripped of their power to become a lowly, gibbering imp, or outright annihilated mind, body, and soul so their arcane makeup could return screaming to the mysterious primordial soup from which the Hells had been born. This gave the denizens of those cities a vested interest in amassing their own bases of power, and that often involved amassing enough mortal souls and riches to place a comfortable buffer between themselves and their enemies. Of course, there was also nothing stopping them from trying to undermine their enemies and taking their
belongings as well. It was a place of backstabbing and politicking and paranoia, pocked by hedonism and reveling in what one has managed to accrue.
Small wonder that several demons chose to try to strike it large in the mortal plane, or maybe even swear themselves to the enigmatic powers of Chaos... or even the Lich King's lieutenants, if they were truly desperate. Such runaways fell under the purview of the Guardian, and most of them were either banished back to their home realm or allowed to go about their business once they'd been made to squirm a bit: more often than not, a scheming demonic entity would slink back to the Circles of their own volition once they knew Medivh was watching them. Of course, not every demon sought to bring ruin to Sylvestrun, and some of them even truly desired redemption: the draenei, the self-named 'exiles,' were examples of this.
The ones that felt guilt were the outliers.
Deep within the alleyways of the magical hub of Mox Nine, a jagged hole in space itself was ripped open, crimson lightning dancing madly around the haggard edges and nothing visible within it but a roiling maelstrom of black-red smoke- at first, anyway. It wasn't long before a lithe figure stepped out, red horns curling down to frame an equally crimson face from which yellow eyes glanced around. "Looks clear enough," he mused to apparently no one, the figure hopping out and brushing his long, black-leather duster to make sure it was clear of the portal before looking down to the curious metal pendant clutched in his fingers. "Hope this thing works," he continued, but this time a little more to no-one in particular; he'd been promised by a friend of a friend of a friend that it was an artifact of the legions of Chaos, a bauble that could obfuscate the Guardian's gaze and allow them to go about their business, whatever that business might be. "Give us free reign of a city of patsies, right?" Mox Nine had something of a reputation for being more tolerant of their kind than fanatical cities such as Stormwind or Orgrimmar; now it was time to take that trust and abuse the hell out of it.
Pun possibly intended.