I want to say that I absolutely detest vampires and their "immortality."
I also want to go on record that I like their idea of blotting out the sun, but no way in hell am I siding with vampires that give out vampire rewards.
…but now I feel like I'm being forced to fight for the light, when I am clearly a child of the night.
Besides, the Dawnguard may not even like the fact that I have werewolf blood.

So much this.
My werewolf will not hunt vampires. She doesn't like them, but she feels a certain bond with them - they're both "unnatural creatures". If she helps the Dawnguard and they rid the world of vampires, what will they do next? Go the same way Vigilants of Stendarr did and turn on werewolves? No, she's not of the light, she's a wolf. She has no part in this war.
I also have a Bosmer ranger/assassin. She doesn't care about vampires. She also hates anything that smells of paladins. And she's antisocial, doesn't care for people around her and does only what's good for her. She will not join those who guard the dawn - not unless the vampires threaten her very life. Will they? If they will, she has a reason to fight. If not, then she'll just move to greener pastures where the sun still shines.
Only one of my characters is certain to join the Dawnguard. And none will ever join the vampires
Gods, how I hate vampires. But this is strictly personal and I know there's a lot of people who will be overjoyed to either join the vampires or the Dawnguard. I won't, that's why I hope this DLC brings something more - new areas, new side quests. It doesn't look that it does, though.