And SOME races may not give a rats buttocks. Sure it may not be wise, but they may not CARE. Besides, to an advanced civilization atomic bombs could be approximately as advanced as stone tools. They may not consider the implications, They may be arms merchants. They may be genocidal. A billion year old civilization may have capabilities that seem god like, but me with a bic lighter may seem god like to a people who are still stealing fire form the sky, as in lightning strikes. If there is a bigger threat sure, I can see why a billion year old civilization would want to hide their traces. But if they are the numeruo uno, they just may not CARE. In fact, if they have lasted over a billion years, then they could be selfish to the hilt, not caring to make grand stands, but also not caring what happens to other species. Also, they will be not wanting competition, so giving atomic bombs to cavemen, would be a perfect strategy for erasing competitors. You won't even have to worry about any OTHER life form arising on that planet to supplant you. Brilliant. The way I see it, if they are hiding, it means there is a bigger dog out there, and that means they are not gods, and if there isn't, they would have no reason to hide themselves.

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