"In our own history that's what happened to just about every civilization when a much more technologically advanced one showed up."
But as our own Tim Worstall has recently pointed out (or was it in his book, I can't remember), extra-terrestrial civilisations will not reckon our resources are particularly valuable and nor will they want slaves who are considerably harder to keep running and less capable than the robots ones they already have. Our value to them will probably be purely the entertainment of watching us.
Then there's the fact that unless we grow out of our yobbish ways, we probably won't last long enough to be that advanced, and so we can probably infer a similar constraint on our would-be overlords. That is, their very existence suggests that they are more mature than we are (or were).
