hes not trying to help humanity grow, he wants to rule it.
You're right in saying that he is not thinking about stepping aside at some point, but I still get the feeling that he doesn't want to rule it for the sake of power (the power hungry Vergil comes out later, and for reasons completely different from the problem of ruling over humans), but for humans' own good (as he sees it).
As for what he meant with "respect", he literally says: "We will RESPECT our subjects, not ENSLAVE them". Now, maybe I'm biased by my philosophy studies, but this phrase can be read as in "we will let them have some degree of freedom", beacuse "respect", if read in connection with "not enslave", can mean exactly that.
Now, if read as such, Vergil's words become less harsh: he DOES care for humans' well being, just thinks that humans, if left to themselves, will not be able to achieve it, so he has to be the one to create a well ordained society in which they can live peacefully, free, not enslaved.
I think this interpretation of his words is better than the downright "he wants to rule just like Mundus, a cruel emperor" one, because it explains how the Vergil we are shown in the first part of the game is not a total facade: he DOES stand for humanity, just like Dante. They only diverge in what they think is good for humans.
And, if I am to be totally honest with you and myself, I think Vergil is right, we DO need a guide sometimes.