We must also consider the possibility that the "aliens" in question may potentially be "reasoning" and "self aware" machines who have already struggled against and overcome their organic creators. Its quite hard to win the argument for "sanctity of life" with a self-aware machine. (In that light, the voyageur message, complete with return address, is a potentially grave error that future generations will dearly regret, with the silver lining that it was sent before we had the tech to nano-encode our genome on the far too revealing message ;) I think central to these thoughts is the consideration of the correlation between advancement in technology and (for a lack of a better word) enlightenment.
Then again, it's probably safe to assume any civilization capable of reaching us would not want to destroy or enslave us -- why would they need to? What power would they gain that they wouldn't already have? True that there is not necessarily a correlation between tech advancement and enlightenment, but what we're talking about here, traveling between stars, is a nearly unimaginable leap in technology. So the correlation is perhaps better posited as immense advancement in technology and lack of interest in destroying a primitive culture.