how can reduceing the dependence on oil be negative and positive? reasons please.?

The obvious positive is that it is a limited resource and if we can learn to not depend on it then it will be less painful when it eventually runs out. There is no question it WILL run out. The only question is when.

Negatives are how we attempt to reduce dependence. One way is to just outlaw it and force people to just get by as well as they can with no help. Another way is to put a really high tax on it to make it painful for people to use so much. There are obvious negatives to those measures. If scientists could find cheap and abundant alternatives that would not be so negative.