Your take on Denethor is entirely wrong, eleanorigby. I suggest hitting the books again. 
Denethor is a wise man. His trouble is that he’s a chauvinist. He sees everything in terms of Gondor. Gondor is it. Gondor is all there is left of the only bit of humanity that really matters. The North Kingdom has bit the Twinkie long ago; it’s people wander around all impotently. No other kingdom of men exists (other than the almost-vassal Rohan) that will stand up to and challenge the evil of Sauron. Gondor has been left with the burden of holding back the minions of evil all by itself, and can’t really expect much help.
And yes, he’s proud. I wouldn’t say arrogant so much as proud. He thinks that the Númenoreans are worth any ten other men. Remember, they still have lengthy lives compared to normal men (Denethor is 90ish when he dies during the War, and both his father and grandfather laid down their lives at 98 years of age), and they have greater ability in most things than most men. Proud and chauvinistic, he simply cannot conceive that it’s at all important that anything survive the downfall of Gondor. Thus, the survival of Gondor is paramount. To this end, anything that can be done to help Gondor survive has his blessing; anything that is tangential to that, or in any way potentially damaging to that he will oppose.
Now, there might be some personal pride that gets in the way of his views on Aragorn; indeed, there is no doubt of it. But it’s not because he doesn’t want to see the True King on the throne. If he really thought that Aragorn, son of Arathorn, was a powerful, mighty man who could take up the rule of Gondor and as a result beat back and defeat Sauron, he would have been willing to let him ascend to the throne (perhaps with some resentment that he, Denethor, had had to be the one to yield control). But he sees Aragorn as Strider: rough, uncouth, truly untested in ruling men (for all that he had accomplished as Thorongil), and just generally not worthy of the rule of Gondor. And he distrusts the fact that Aragorn is firmly in Mithrandír’s camp, because Denethor understands that Gandalf does NOT thinkg Gondor is the be-all, end-all of civilization. Gandalf sees Gondor as simply one part of civilization; this view of Gondor Denethor rejects. So any northern chieftan who is helping Gandalf probably doesn’t think Gondor is the most important thing in the world, either.
But some important things should be noticed about Denethor in the books. Saruman, supposedly an almost infinitely wiser being (since he is a maia), is ensnared to Sauron’s will through use of the Palantír. Denethor never is. Denethor is betrayed by his USE of the stone, since Sauron manages to control what Denethor sees, to shape his worldview. But Denethor is puissant enough to retain control of his thoughts, and continue to reject the direct influence of the Enemy. Only Aragorn manages to do more with the stones, and at that, only after a massive tussle during the night while still in Rohan. Thus, Denethor must still have at heart a basicall “good” nature. Proud, yes, but proud because he is powerful, and intends to defend his people against a seemingly overpowering force of Evil.
And it is not that much of a shock that such a man would tend to favor a son who is many of the things he himself is not, who will be able to be a great champion in defending Gondor. That hardly makes him an evil man.
Oh, and by the way, I, too, would love to see some citations to examples of Aragorn being all full of “overt pride.” A man full of overt pride doesn’t sit in the back of a crossroads inn and watch everyone silently, without any of the patrons having any idea who or what he really is.
But I’ll bow out because I don’t want this to become a pissing match.