I think it's unlikely that space aliens, if they exist, would come as conquerors. For one thing, with the whole universe to roam, what would a two-bit planet like ours have to offer anyone. I do see two trouble areas. One, they might be interested in studying us, and they might hurt us by accident just as we might step on an ant. Two, they might have a vested interest in keeping us out of space. As long as we lack FTL drive, we're no possible threat to them, but if we develop FTL without controlling our natural savagery we COULD be a major annoyance.
