An Alternatively Evil Snape

Curious Jew in her recent post, Severus Snape is a Good Man, makes a case for assuming that Snape is good despite the fact that, as everyone who has read HBP knows, he has murdered Albus Dumbledore. Like many people before her, CJ argues that Snape must have been acting under Dumbledore's orders. Her makes two arguments. She brings the precedent of Jon in A Clash of Kings, who goes over to the enemy in order to save his life and fulfill his duty. Her other argument is that it would be plain stupid if Snape really were evil in the end.
I find it ironic that CJ, who bashes the Potter series for being derivative, should suggest that Rowling should do what George Martin has already done. As for the issue of finding a way to have Snape being a villain and maintain Dumbledore's credibility. I do assume that Snape is evil though I do not assume that he is a straight follower of Voldemort. Rather I would suggest that he is allied with the wizard nobility party, the Malfoy's and other wizards who wish to maintain the "old" order. These people supported Voldemort because they believed that Voldemort would solve their problems for them, get rid of the mudbloods and anyone who did not agree with them. They had no objections to abandoning Voldemort when he lost power and I would suggest that now that he is proving to be beyond their ability to control they may be seeking to bring him down. Dumbledore's mistake, like that of the readers of the series, was that he assumed that just because Snape was against Voldemort and protected Harry he must, therefore, be on the good side. Snape needs Harry alive because he hopes that as long as Harry still lives Voldemort will be focused on him and could, therefore, be kept from destroying the wizard nobility party. Harry serves this purpose better than Dumbledore because, from Snape's perspective, Harry is not a real threat like Dumbledore was.
Rowling, I believe, has managed to pull the wool over millions of her fans by getting them to focus in on Voldemort as the central villain. Throughout the series, Voldemort has been, for the most part, in the background and the villains that we have had to spend most of our time on are the Malfoys and Snape. Yet we have not treated them with the proper level of seriousness because we were focused on Voldemort as, pardon my Buffy, the "big bad." It was this wizard nobility party that created Voldemort. Voldemort by himself is just a brilliant seventy-year-old angry teenager with father issues. (This is why it is so important that Dumbledore called Voldemort by his name, Tom Riddle when they met and why Rowling has put such an emphasis on the Riddle side to Voldemort's character.)
I do not believe that the story arch for book seven is simply going to be Harry questing after the remaining Horcruxes, culminating with a final battle against Voldemort, in which Harry manages to overpower Voldemort and destroy him. The main purpose of the quest after the Horcruxes is for Harry to learn the lesson Dumbledore was trying to teach him in HBP, that Voldemort is not a god. Behind everything, he is just a flesh and blood wizard. Meanwhile, we are going to discover that the party in power at the Ministry is in many respects quite similar to the wizard nobility party, if not the same entity under a different name. Voldemort is going to slaughter a whole bunch of these people, including those who are actual Deatheaters. This though is going to weaken Voldemort. He has Harry's blood in him, which carries the sacrifice of Lily Potter. As Voldemort isolates himself more and more and demonstrates that there is no one whom Voldemort loves or would be willing to sacrfice himself for. A major turning point in this regard is going to be when Voldemort allows either Nagini or Bellatrix to die, beings that Voldemort might possibly have loved. Harry will destroy Voldemort by demonstrating his willingness to sacrifice himself for Ron and Hermoine. (Ginny will die.) This will not, though, be a good triumphing over evil ending. The wizard nobility party will still exist and they will still be in power. We will forever leave Harry, Ron and Hermione with them realizing that, having overcome the schoolboy level task of defeating Voldemort, they will have to spend the rest of their lives fighting against this wizard nobility party, something that cannot be done by mere force of magic. This will be Dumbledore's true legacy to them. He never sought power; instead he built a school. Harry and his surviving friends are going to go out into the world as members of Dumbledore's Army and fight the everyday evils of the world.