I cringe at the term "invasive" as it implies intent on the part of the plants. In the natural world, plants and animals fill available niches. Often, niches are available because humans have destroyed the native habitat or thrown it so far out of balance that 'all bets are off". The plants and animals that move in are aggressive colonizers for a reason. IMHO, that reason is to populate the barren or disrupted ecosystem rapidly and establish some kind of balance again. After severe disruption, such as urban development or crop cultivation, it is difficult or nearly impossible for a balanced ecosystem to be reestablished. The "cost" of "invasive" plants and animals is measured in the effect they have on the economic activity of humans. IMHO, the rhetoric about these plants "destroying" ecosystems is pseudoscience. They do not invade balanced or pristine natural ecosystems, but rather (human) disrupted environments. Natural systems will absorb new species and, in the process of time, integrate them into the ecosystem, but that is only if the ecosystem in question is healthy and generally balanced already. A monoculture or severely disrupted ecosystem (lawns, parks, cropland, abandoned lots, overgrown previously developed areas, etc.) is not an honest venue to assess whether a plant or animal is "invasive".
That being said, when planting new plants, gardeners need to be responsible and realize that their gardens are not balanced ecosystems. Because this is true, seemingly innocent or harmless plants can demonstrate their ability to be aggressive colonizers in such an environment. So the gardener must maintain the balance with deliberate work, or the plants will make their own balance whether you like it or not!
