Strawman. GP was saying 'don't buy overseas seeds because they are species that are not native to wherever you are importing them to'. Which doesn't make sense - whether a species out competes another doesn't depend on where it's from. Sure, when you introduce some species into certain ecosystems, those ecosystems will change. Nobody's saying you shouldn't think and/or manage. What I'm saying is that the whole 'exotic is bad' line of thinking ultimately boils down to the naturalistic fallacy.

Exotic is bad when it costs the US economy $167bn a year, which is a realistic estimate of the amount lost because of the effects of invasive species of all kinds.

If you think that's a "naturalistic fallacy" perhaps you need to brush up on your economics.