imho there's a kind of unfortunate essentialist philosophy which runs rampant among some "ecologists" and which has seeped into the public sphere... which believes that "nature" is a self-balancing system, and it is only our interference (as something "outside" nature) that breaks this. And this gets tied into the "natives" vs "invasives" dialog, as well. I think this is profoundly wrong. Nature is chaos. (Said in Werner Herzog voice, or something).
Consider that the ice age only ended just over 10,000 years ago -- which is an extremely short time ago in geological and evolutionary terms -- and every forest, meadow or natural space you see in (temperate North America and Europe at least) is very new and was "invaded" after the glaciers melted and as the climate warmed. In some cases quite recently.