I enjoyed Bob's piece on alien abductions vs. time travelers in the April Phactum. However, time travel poses so many metaphysical questions it makes the head spin, as many sci-fi writers have noted. If the TTs were to change the past to prevent the crash, in what unexpected ways would they alter the future? Can they even, indeed, truly alter the past -- or is their voyage back in time to change events itself an unalterable part of the past? This is the modern version of Predestination vs. Free Will on which Calvin and so many other theologians cracked their weary brains. Recall that in conventional Christian theology, one of God's main attributes is that He is outside time, like Bob's hypothetical (I hope) TTs.
"They could opt for a more confrontational approach and come in blasting away ... the area 51 personnel wouldn't stand a chance." True, but it would create one hell of a stir. Surely the most efficient way would be to go back in time and prevent the parents of the inconvenient persons from conceiving them, a la Back to the Future and many similar fictional works. But that raises the question of whether someone else would simply be stationed in their places. If one were fated to encounter someone at the crash site, would it have to be a specific someone? Now you see why Calvin was such a sour, gloomy individual.
I don't see why alien abductors or TTs would be satisfied with only a thousand samples of homo sapiens to learn anatomy, any more than science teachers are satisfied with only a thousand frogs. Maybe the visitors, whether ETs or TTs, are the equivalent of sophomore biology classes on field trips. Every student gets his own human on which to experiment. I suppose we should be grateful they don't pith us, although with some of the alleged abductees, how could we tell if they had?
Theories about alien contact have an implicit fallacy at their core -- they assume that aliens would recognize us as an intelligent species worthy to be treated, if not as equals, at least with respect. Is it possible that advanced creatures from other worlds might look at our cities, roads and bridges with the same attitude with which humans view a bowerbird's nest or a honeycomb, and listen to our languages as we interpret bird calls and wolf howls; as products of instinct? I forget who said that when an animal does something we call it instinct, and when a human does the exact same thing we call it intelligence.
As for why the ETs have never tried to reclaim the bodies of their comrades at Wright-Patterson: Since, as far as I know, no one claims to have inspected these bodies recently, they may not be there anymore. Maybe the ETs already sneaked in and took them home.
Or maybe the ETs have a complex theology in which when good ETs (or bad ones?) die, they go to Earth. Or maybe they just don't care; even among humans, customs concerning the disposal of dead bodies vary widely. A friend of our family donated her body for medical school dissection; maybe the ETs believe that starring in an "alien autopsy" is the best possible use that could be made of their remains, and thus they kindly ship them on to us.