I always thought that Bethesda herself wanted the Dragonborn to go evil. Just look at the trailers. First, we have this epic Nord wearing Studded and Iron Armor fighting a dragon. He is supposed to be the good guy there. But then, Dawnguard comes out and we see the same person being an evil Vampire. Well, since the Dragonborn has the blood of a dragon, he will always search for more power. It is in his nature. But I still couldn't forgive the original Dragonborn if he'd do that. Paarthounax IS a dragon, but through medidation he has overcome his "evil" nature. Why couldn't the Dragonborn do the same? I am pretty sure Bethesda made the Dragonborn to be a d*ck.