I can see that. We have no idea how nuclear or atomic detonations affect others in the neighborhood so that is a possibility. I would argue however that an enlightened society would necessarily have a non interference policy, even if it meant letting us destroy ourselves.
Who says they're enlightened? Are third-world and muslim countries enlightened because they've come into possession of our modern technology?
Obviously not.
And who says there's only one race, or civilization watching us? There could be many, and they wouldn't necessarily all have the same code of ethics.
If you can believe many of the reports in the UFO literature, a lot of these ETs have no compunctions about interacting with humans, or with revealing themselves.