Why Would ETs Come to Earth?

One of the reasons to be skeptical of the claim that extraterrestrials are visiting out planet is, as pointed out by Orac and many others:

First, if there really are extraterrestrials of such awesome intelligence and possessing such incredibly advanced technology, why, of all the places they could go in the galaxies, would they spend all that time, energy, and technology to travel to earth?

Maybe they're here to study a mass extinction caused by primitive technology. Complex ecosystems can be studied elsewhere. Mass extinctions caused by comets or volcanoes can be studied elsewhere. Mass extinctions caused by advanced technology can be studied elsewhere. But this is the only place in the galaxy where DDT producers can be studied in their native habitat.

It makes at least as much sense as “they want to protect biodiversity” and it hasn't been overdone yet.