I believe people who are abducted by aliens are, in fact, aliens themselves. They've been dispatched to our planet to serve as recording and monitoring devices. Their periodic "abductions" are for the purpose of taking them back to their mother ships so the data they've absorbed can be downloaded into the ships' computers.

Of course, the "abductees" are totally unaware of their own true identities. Before they were dropped off on Earth, their memories of their alien lives were erased and replaced with suitable sets of human "memories".

When you look at it from that perspective, a lot of stuff about Shane McBride falls right into place, doesn't it?