are warlocks inherently evil
i dont think kael was insane, just power-hungry
he craved what illidan wouldnt give him, so he turned to kil'jaeden and got it from him instead
depends on the individual warlock
all warlocks are power-hungry to some degree
some do it for the sake of dominance alone
others use it for a 'fight demonic fire with demonic fire' mantra
any warlock who succumbs fully to corruption is looked down upon as disgrace and a failure
discipline is a key trait that must be practised by all faction-aligned warlocks lest they find their head on the chopping block for going too far and succumbing
I imagine many see it as a sacrifice for the greater good or as a method to master what seeks to destroy us all.
The warlocks that are part of demonic cults (they usually show up for "kill X cultists" quests) are evil. The power that warlocks wield is not inherently evil though. Fel magic is a tool, and like any tool, it's as evil as the one who wields it.
The arcane magic that mages use is actually a highly regulated version of the magic warlocks use (unless that got retconned when i wasn't looking). The Kirin Tor outlaws magic that has a high chance for abuse (e.g. necromancy).
The playable warlocks are typically not evil. You'd probably find the highest concentration of faction aligned evil warlocks among the Forsaken.
Whether using fel magic inherently corrupts the wielder is debatable. It could be that since the practice is outlawed by the Kirin Tor, only the morally challenged pursue the craft in the first place(i.e. if guns are outlawed, only outlaws will have guns). Some uses of fel magic could be considered inherently evil (e.g. binding souls), but the basics of the magic don't imply a morality; for example: if a mage blows up an orphanage with a fireball, the fireball itself isn't evil, nor did that fireball whisper into the mage's ear that those orphans totally had it coming.
Sorry if that rambled a bit; it's past midnight here, and I need to get some sleep.
TL;DR: fel magic is no more inherently evil than necromancy. It's easy to abuse to evil ends though. Just remember, that's not grandpa's corpse plowing the fields for us; it's a conveniently humanoid shaped hunk of inanimate tissue that doesn't need food, water or sleep.
As for Warlocks, you can be one and certainly not fall on that sense. Just dabbling in these kinds of dark magic doesn't mean anyone is somehow being harmed. And if they are, many other people, non-Warlocks, who wouldn't be considered "evil", would harm others in the same way.
On the other side we have light users that aren't "good" either. Scarlet Crusade is totally based around the belief of in the light, still they turned to be the worst kind of person.
Warlocks might not be altruistic, but non-Warlocks aren't automatically good merely because they aren't Warlocks.
Also, you can be considered a Warlock without the need to dabble too deeply into dark magic. Summoning demons aren't really evil. At all. It's just making use of them for whatever ends that might be evil or not. It might not even be considered evil for the demons themselves, because some of them make pacts willingly.
Aside from that, "evil" and "good" are concepts quite oversimplified. Things are more complicated than that.
They're warlocks because they're evil and amoral.
Illidan and Kael'thas already had everything they needed to become crazy, and did. Once there, they had no problems experimenting with magic.
Initially a warlock may be a wide eyed, plucky youth absolutely convinced that demonic magic is simply misunderstood. That despite EVERY SINGLE MAJOR USER OF IT EVER ends up stark ravingly evil, they're convinced that they, THEY will be able to wield the darkest power in existence without succumbing to its corrupting nature.
Inevitably, however, the natural order of magic takes its course and bit by bit the user will ultimately slide into depravity. Fel magic just isn't another form of arcane, it's manifest EVIL, and not even SARGERAS was able to deal with it indefinitely without turning to the darkside.
In the end, it's only a question of time.
Edit: And Illidan is a case in point. I don't think he's evil.
Warlocks are really no different than mages, druids, shamans, or priests in that they call on power from a different plane in order to empower themselves... it just happens that warlocks call upon demons and fel energies which can have corrupting properties.
I would say yes, if you deal with demons or use their power in any way shape or form no matter your intention, you are evil. To use Warlock powers you have to do deprave things.
Nhh, I wouldn't say it makes them evil. It depends on how they get the power to begin with, for example Demon Hunters use fel magic yet they aren't usually considered evil (with exceptions such as Illidan).
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