Christ, we've only just found water on the damn thing and already you guys are talking about raping its resources. Granted, we might not find the Na'vi skulking around Enceladus' subsurface seas but at what point is interference with a planet's biosphere justified? Bear in mind that intelligence and sentience may occur in many forms besides the ones we recognise. Ideally any law of non-interference should extend to any planet with indigenous life, meaning that if we want to colonise and exploit other worlds we need to terraform ones that are confirmed lifeless. But that won't happen, of course.
Like 1984, Avatar is a warning about the nastier aspects of human nature, and like 1984, one that will be either ignored completely or used as an instruction manual when the time comes!