If one think that it's ok to kill and selectively (completely?) annihilated a group of bugs because most of them are considered as the cause instability or chaos or ruining what's around them (according to one particular species who thinks they're smart enough to decide what's bad or good) I think it's very understandable that there'll come a time when a pack of creatures from outer space trying to annihilate human beings from the earth.
I don't know.
Maybe some rats are just there to enjoy the life, you know? Ponder about great things they can do to make the world better, help other rats to achieve whatever achievement considered by their kind, care about their young ones, coexist with other fellow pest. Maybe they're trapped in a system where they have no choice but to live as what people considered as pest, because that's what are expected from them by their kind--thinking that it's their nature to make people suffer. Maybe there are some of them who actually bad, but the rest are silent majority that live their life without being considered as different than the bad ones.
But of course not.
They're rats.
Rats don't have life. Right? So it's ok to think that we can kill them. Or wanting them to die.
So does cockroach. Or moths. Or other creatures that are considered as pest. Whatever. They deserve to be get rid of. They aren't nearly as smart or resourceful as some other creatures, what's the point of keeping them around? They're only there to damage what's around them. Losing them wouldn't be a big deal.
(If the aliens are coming, I called it. But I think there's a greater possibility that they actually believe that human being will annihilate themselves without them having to send trucks, so.)