Fact: Demona is not trying to destroy humanity just because she wants to save her kind. That's the cover story and what she's convinced herself. But really, humanity is her scapegoat. She knows, deep inside, she fucked up. But she won't ever admit it.
"What have I... what have they done to you."
Myth: Demona isn't power hungry!
Fact: Actually, she is. We have seen this played out a few times. For one thing, even back in 984, she was encouraging Goliath to take control of the clan from Hudson (very Lady Macbeth). She also learned sorcery because it was a key to power.
And, of course, what she said to her younger self in "Vows" "Rule the gargoyles, rule the world." and in "Hunter's Moon:" "I will take my rightful place."
Make no mistake, when humanity is gone, she wants to be on top of the pecking order.
Myth: But what about Angela? That's proof Demona is a loving teddy bear!
Fact: Yes, she does love Angela. But does she respect Angela? I think the answer is definitely no. If anything, Angela's existence is going to be Demona's new justification for all her actions. Her new excuse. Remember, the next time they saw each other in "Hunter's Moon," she was going to commit mass genocide and she cited Angela as one of her motivations.
"The spell will protect me, my daughter and my kind from the plague."
Notice how she still put herself first.
Myth: She lives in a beautiful home called Destine Manor.
Fact: There is no Destine Manor. I don't know where that name came from, but it crops up a lot, and it's definitely not canon. And it's most definitely not a manor. It's a townhouse in Gramercy Park. Not an estate!
Myth: Demona's pissed off because she's horny.
Fact: This justification is beyond brain dead.
Myth: You're just locked into a two-dimensional view of things? Why can't a hug from Angela, or interacting with humans change her?
Fact: Re-read all of the above. She is a very three dimensional character, and that's why I love her. But her shade of gray is very, very dark.
Myth: But she is an anti-villain! Maybe even an anti-hero, not a true villain!
Fact: Demona is actually not an example of the anti-villain trope, but a big point is made about how she thinks she's a clear-cut well-intentioned extremist, when she isn't. It's like we've got this rather juvenile concept, that just because a character doesn't sit atop a throne of skulls or occasionally shows genuine human emotion now and then they can't be "really bad." The truth of the matter is that Hitler really did love kids.