They are more or less like the Vigilantes of Stendarr and the Silver Hand. Bad people claiming to be good just because they hunt vampires. But they are extremely prejudice, torture people(just check out the dead werewolf bodies in both human and beast form, and torture tools in their lairs and even a http://www.uesp.net/wiki/Skyrim:Physicalities_of_Werewolves on dissecting people!). Not to mention, hypocrites. I.E, "we serve the god of mercy but we have none to spare. Walk in the light or we will forcibly drag you to it".
In the end, it is all a point of view.
What exactly draws you to this conclusion about the Dawnguard when we really nothing about the faction. I know the Vigilants of Stendarr are extremist as they will kill anything or anybody as ling as it pertains to Daedra in any way but they have been touched upon in the base game.
Anyways I am curious to wee how the winged vampires will be explained in this game because to my knowledge they have never been mentioned in the lore at all. Hopefully they are the Volkihar vampires, if not what are they and how do they fit into the world, and I am curious on the more intricate details surrounding the Dawnguard and the vampires and what history they have with eachother. I am also curious will we get an entire actual island to explore, also I hope we get the old spells we have lost at least back to Morrowind and I want spell creation as well.
Now for some smaller things, how many new weapons, armor, and clothing items will we get, what about general junk for us in game hoarders that want to decorate our houses. Is there an options to change your hair, beard, face paint, and your dirt level.
Also I wonder is this a proper expansion pack and not a quest line DLC similar to Knights of the Nine.