Harper would not be a cancer for the Braves; with the one exception of the insane Jonathan Paplebon; Harper's teammates and his managers all like him. Even so, not sure Harper merits the big payday that is coming.
As Harper has grown into his mid-20s, he has lost speed which has impacted his defense (below average defender) and his base running (average at best base runner). IMO, to pay one guy $30 million+ a year, he needs to do more than hit the ball out of the park. Right now, Harper is a limited player, and only see his limitations becoming more pronounced as he ages. Taking all of those factors into account, it's just not worth the massive long term investment. There is a reason that the Nats haven't made a concerted effort to reach a long term deal for Harper, like they did with Strasburg. With that said, easy to see Harper hitting 40 HRs next year. There are a lot of teams that think the missing piece is a middle of the order left handed power bat; Harper can fill that void.