The problem when discussing the probability of technology-capable alien life forms is that we forget how very unlikely our own brief existence is. We forget that were it not for grass, our ancestors would not have come down from the trees. We forget that nearly all intelligent life on Earth is aquatic, and you can't mine, smelt, and fabricate tools inside of a liquid solvent. We forget that nearly all intelligent life on Earth remains non-technological either because of environment (cephalopods, cetaceans) or physiognomy (corvids, elephants). So we extrapolate from our astonishingly unlikely existence and conjure up Star Trek nonsense that leads us to dramatically over-estimate the probability of equally unlikely occurrences. Now add in distance and time, and the chances of any two technology-capable species overlapping are essentially zero. As for fantasies about robotic quasi-life entities, these represent a similar set of intellectual errors.