Well, the main problem with invasive species is not that they shouldn't be at a certain location because of some sort of divine order or xenofloraphobia (i.e. fear of weird plants) but because they, in many cases, will kill off the native species, taking the place of plants eaten by native fauna, thus possibly leading to a collapse in eco-systems. This problem is already prevalent in some parts of both North-America and Europe, where a certain japanese plant has been brought in, reproduced in the wild and now quickly chokes out all other plants. So it's not because 'we hate strangers' or it's better for the earth, but because it's better for the ecosystems. If you'd introduced exoctic plants, you'd be needing to introduce more species as well as natural enemies. But since they might thrive as well, you're probably in an even bigger mess once you start experimenting with stuff like that.