At the same time we see that Demons care about "protecting the cosmos from the Void" only when it's a Fel Titan telling them to do so. Otherwise they only care about destruction.
Demons are so inherently evil and despicable that Sargeras literally had to corrupt an entire race of Arcane users to act as his top strategists, because he couldn't rely on the demon brutes.
Because they are """"good""" only by virtue of fighting the Legion alongside other Order halls.
While in reality they're all power-hungry and shady individuals, the thirst for Fel by nature is insatiable. And thus as per the facts, the term "good" here is used very loosely.
And depending on how you RP your Warlock, even the PC Warlock is a fucking repulsive individual. He could be both a Warlock and a Sylvanas loyalist, one of the most scummy and vile mortals imaginable
Don't tell me that someone would play a warlock and a Sylvanas loyalist to be the good guy