It might have something to do with the problem of determining at what point is something "native."
This essay titled "Re-thinking Invasive Plants" (http://www.prodigalgardens.info/reth...e%20plants.htm) discusses this point in more detail. While the essay focuses on plants, I'm bet some of it could apply to animal and fungal species as well.
The essay relies a bit too heavily on the (unsupported) Gia hypothesis to build its argument for my taste and takes a somewhat laissez-faire approach to land management. But at times, knowing when to be hands off could be important. Maybe we can use what is being dealt out of the biodiversity deck of cards for society's benefit as well.
It brings up a number of interesting questions, so its well worth a read.