Invasive Species

What exactly is an invasive species?  Here is what wikipedia says it is: An invasive species is a plant, fungus, or animal species that is not native to a specific location (an introduced species), and which has a tendency to spread to a degree believed to cause damage to the environment, human economy or human health.  So is buck thorn an invasive species? What about garlic mustard? Am I doing the right thing or the wrong thing when I pull garlic mustard and send it away in the trash to a landfill? Are my actions as the steward of the property that I (almost) own causing damage to the environment, human economy, or human health? If so, if my actions are causing damage, does that mean the garlic mustard should stay and I am the invasive species?  I have European blood. I invaded this corner of paradise. Are my actions causing damage to the environment? Am I helping or damaging human economy? Am I helping or hurting human health? I joke about that bird house gourd vine trying to kill me but maybe, just maybe, I am the invasive species and I should leave the buck thorn and garlic mustard alone. I think the great Doctor Suess wrote a book about this very topic.