I think either aliens are not responsible for human mutilations, or they do it to drive us crazy, or they do it for kicks.
Maybe they're alien cultists (we got waaay crazier as we evolved, so why not them?).
I'll go out on a limb and piss
everybody off by saying I also think the phenomena which can plausibly be ascribed to aliens are not necessarily evidence of being particularly advanced (I mean technologically - there's no evidence whatsoever of any particularly elevated ethical thinking).
I think a lot of what is and has been reported for centuries is something much stranger than aliens. Perhaps just reality farting, if you like. But I also think it's perfectly plausible that in addition a generation ship arrived in our solar system in the early 20th century, possibly carrying refugees who may have
lost scientific knowledge over the centuries of travel for all I know...think of how much changes if they were in relatively small numbers with no way of returning home. And think of what knowledge and practical experience could be lost by a culture that spent a few centuries in deep space.
for instance, perhaps the answer to the question "if they're so advanced, why did they have all those crashes?" is that they no longer had any direct knowledge of flying in a planetary atmosphere, and it took time to learn and to adjust their technology (perhaps Foo Fighters were probes recording the flight characteristics of terrestrial aircraft). The triangles might be the result of such study and adaptation.
Oooh I like that idea...they reverse-engineered our technology
If such a people or a faction were carving up the locals, it could simply be crude research or even human sacrifice.
What I'd
like to believe is that we're dealing with a civilisation that can bend space and time to cross the void - because it would mean that that's possible and we might one day be able to do it ourselves. But just because I want that to be true is no reason to believe it is.