i think its more about having no natural enemies that hinder plants at going totally crazy.

for exampley if a tiger is put in the zebra cage the zebras have a problem and nothing will hinder the tiger to kill them all or reduce his killing to a natural balance where zebras have the chance to be population stable.

i have friends working in biology and they have no problem with new species in new regions if the adapt well and are prepared for the future or in other words make the ecology more stable.

but I get your point. many people are viewing it as black and white and have extrem opinions