Rewarding someone when they do what you want is just as sleazy and manipulative as punishing them when they do what you don't want. It might be the fact that a child doesn't realize that, but an adult undoubtedly (eventually) would, and be just as resentful.
Reward works well for building a healthy rapport and relationship. I don't think punishment is entirely ineffective, but if it isn't rare and judicious it may well end up causing more harm than help. The problem is that the response to punishment is visible immediately while the downsides may only appear many years later.