As a fan of shows like Dexter, your sociopathy comment leaves me wondering... any aspiring serial killers who would operate at such a scale? Has it already happened? We seem unable to deal with such threats, since it hides intent so well

That's a disturbing thought...

What I meant wasn't that poisoning the population has been anyone's first goal, but that they have just callously disregarded those effects in pursuit of profit, or of "success" in whatever hierarchy they inhabit.

I have to imagine that this is almost always paired with rationalizations. But maybe there are especially-alien mindsets that don't have to do this -- the "true sociopaths".