You make some interesting points, but it seems like a stretch to generalize our psychology and physiology to the entire universe. Time is long and space is wide. Perhaps civilizations that manage not to make themselves extinct in the earliest millennia of their mastery of tools tend to lay much longer term plans for the exploration of space. Long term as in hundreds of thousands of years, which is still peanuts compared to the time required for inter-stellar travel. Could civilizations not evolve whole portions of their populations to be adapted to it? For instance, they could breed themselves to be semi-aquatic so they can spend most of their time swimming in pools where most of the gravitational weirdness would be moot. Or breed themselves to deal with warped gravity directly. By the same token, one doubts that a civilization planning inter-stellar exploration would send out a few guys in a flying tin can as we do. It wouldn't make sense. Voyages of hundreds of thousands or millions of years would space for a large breeding population of inhabitants and vast resources. It would require craft the size of cities at least, probably travelling in clusters to minimize the probablity of a disaster wiping out the whole project. So I don't think your argument applies to the scale of endeavor that inter-stellar flight would require. BTW, I'm not convinced that there are little green people within any distance of the earth that could matter. One suspects that intelligence is a self-limiting phenomenon.