To my mind, being manipulative and being a good guy are not mutually exclusive traits...
I would agree with this for the most part. There is also the road to hell aspect of well intentioned manipulation. I would actually think it a good thing if in this story Dumbledore's intentions are noble even if his methods might not always be good.
Yeah. I do not care for Snape. He is a grown man who gets his jollies of verbally abusing, terrifying, and ruining the educations of nearly two decades worth of children. While I do concede that he had a role to play it did not require that he be a fucking asshole to children or nurse a grudge to such an insane degree that he takes out his aggression on the child of his school days nemesis.