Up where I live there are zebra mussels and round gobies and everyone said the lake ecosystem would be destroyed. But that never happened, instead what has happened is farmers have fertilized the crops and it runs off into the fields and into the lakes and then there are algae blooms which produce toxic algae. The toxic algae was produced from man not from the zebra mussel or the round goby. They like to say it is because of invasive species but the truth is that it is man that pollutes the lakes and destroys nature. The same is true of lionfish, man has overfished the ocean leaving a lot of small fish to multiply and since the lionfish can not be fished commerically it survives and increases in population size because there are so many small fish due to lack of native predators.
I really wish there could be a way for divers to go to a remote place in the Caribbean like I did in Belize and see for themselves that if nature is left alone it does just fine. The lionfish problem is tiny compared to the destruction that humans do.