It's as much an assumption as pretty much everything else about his character, unfortunately.
Just because Vergil did not outright state his reasons doesn't mean he did not have any.
Therein lies the problem, because he never states his reasons. The game tells us he's hungry for power, and then...nothing. No motivations for it, just..."gotta get power".
He also clearly said that ''without power, you cannot protect anyone, let alone yourself''. This implies he has something to protect (now or in the future). It could also mean he's traumatized from the death of his mother and wants to create a 'fairer' world. A bit of reading between the lines can get you a lot farther than just denying he has any reasons.
That is something he says
to Dante, the guy who has made it his life to hunt down demons and help people. Vergil was extolling the virtue of the power he covets while mocking Dante's own motivations in life. Everything else you said is conjecture, which is the gigantic problem with Vergil - so much of him is left unsaid that there's only a few solid facts about him.
6 He only says that when people are around... so I'm not sure that's his real motivation. And even if it were, it's a perfectly acceptable one. ''Never told why?'' Have you even watched all the cutscenes? One of DMC's themes is that demons obsess over power while humanity (or Dante) gains more power because he doesn't obsess over it. Disliking that theme does not make it less valuable.
Whether he only says it around others is irrelevant. If we as the audience aren't presented with things to solidly associate with his motivation, it's difficult to ascertain what his motivation is. If his motivation for getting more power is simply "he's a demon", then holy sh!t that just makes it worse.
7 Yes... well, when you think about it, doesn't that mean what he's doing might be a good thing? I'm guessing that... he wants to close the gate so demons can't hurt humans anymore. He's probably doing this out of a misplaced sense of respect for his family. He doesn't want anyone to go through what he went through as a child. Just because he doesn't literally say ''I don't want demons to hurt anyone anymore... you see I'm traumatized blablah'' doesn't mean he 'has no motivation'. I'm glad he didn't outright say it and start a sob-story about it. Let DmC handle unnecessary obviousness. No offense intended! I like DmC!
What makes that a hard pill to swallow is that Vergil jeopardized humanity
more by raising Temen-ni-gru and releasing demons all over the city, all so he could open a portal to the underworld (objectively allowing
more demons out) so that he could get the power that Sparda had a damn good reason to lock away in the first place.
The problem is that we
need to hear that motivation. It doesn't need to be spelled out obviously, and there are plenty of ways to divulge that information to the audience without an obvious and out-of-place blurt out, but the fact is we didn't get anything at all. The game actually seems to pick up halfway through the brother's quarrel, as if Dante and Vergil have already started down on their separate paths, as if they had already had it out once explaining why they felt the way they did, and what their motivations were. So it's like we picked up the story in the middle, and they're done explaining why Vergil feels the way he does, and we're just left going "Wait...why?"
8 Don't remember him implying that. Sure, he fights Dante seriously, but if he wanted to kill him he would have. Seriously, he lets Dante get away multiple times, even in the beginning (when Dante had no devil trigger). He could have cut off his head... only he didn't. In fact, he allowed Dante to Devil Trigger. So you still think he intended to kill Dante? I think he wanted to demoralize him and keep him off his back. Even the final battle mightn't have been to the death. We don't know. All we know is that he wanted Dante's piece of the amulet, and I doubt he needed to kill him for it.
He straight up tried to murder Dante by impalement in their first encounter. Vergil was surprised that Dante survived, thanks to his Devil Trigger it would seem. They were ready to leave him there to bleed to death, and then upon their
second encounter, Vergil mutters that he'll just bleed Dante dry to get the mechanism to work.
9 There is no indication that he despises his human heritage. He never talks about it. Yes, he wants power, and to be as demonic as possible because he thinks demon stuff gives him power. But does he want to relinquish his human side? No indication of that. Again, he probably wants to be more like pops, since he has an entire library on Sparda remember? He keeps reading up on his legacy, so obviously he respects Sparda's 'human' side too. The emotional side of him that protected humanity.
Vergil didn't have an entire library on Sparda O_______o He was just in one where he met Arkham. Anyway, it's a very real possibility that Vergil doesn't care at all about Sparda's human side either. He constantly hears about how his father was
really powerful, and that's the only part he ever seems to care about. Like Wolf said, Vergil even goes out of his way to undo what Sparda did to protect humanity - shutting the demons off from the human realm.
I'll question this till the day I die, because everything that he does in DMC3 shows that he has no respect for anyone, kills people (sometimes when they are defenseless) whenever they are useless or in his way, and doesn't show any care for anyone but himself. Well, and some slight begrudging care for Dante at the end when he falls off the waterfall, but even that was after he tried to kill Dante for a third time >.<
The only respect Vergil ever shows is to the idea of a fair fight; he doesn't like guns because they don't require the fortitude or strength as anything else, and therefore sully the idea of two people engaging in a battle of pure ability. That love of a fair fight even plays into his ideals for power, since a pure and unadulterated battle is a show if ones' power.
Then again, despite liking fair fights, he still kills people who are defenseless, so even he is willing to compromise that belief to suit his own agenda. He even used a gun because it would serve to get rid of a roadblock ahead of his goal.
You say old Vergil has no motivation, but when I think about it, what is new Vergil's? He just always wanted to rule Limbo? I mean, doesn't he have the same motivation as old Vergil, basically? So... dafaq we talking about? XD
DmC Vergil's motivation was to get revenge on Mundus for ruining his family, and usurp the demon king's position as ruler of the Earth, because he felt that human's were weak little children that needed protecting, and the only ones fit to rule them was the nephilim. That is something we explicitly know because the narratives tells us as we continue through it.