In a previous life I used to do lake assessments for stocking trout. I have seen the damage some of the animals listed on the link have done. In particular red shiners, and milfoil can change an ecosystem of a lake, making it more of a monoculture with large mats of invasive plants, with only the invasive fish doing well because they live in that choked environment now. If a lake is part of a network of lakes and slower rivers there is nothing you can do. If the lake was somewhat isolated the only way to get rid of the invaders was to kill off all the fish in the lake and re-establish new populations with native fish. In the 80s we used rotenone for that task, I don't know if it is still used.
Responsible fish keepers should not release their fish into the environment, but in reality, many people will especially if the choice is between a release vs euthanization. Plants are even more insidious, because they can be released into the environment more easily, even with a simple water change if the waste water ends up in the natural environment.