It's hard to disagree with the fundamental stances of the two previous posts. I would suggest that one of the reasons why there was a great ecological harm is that European Exploration helped to start the process of eliminating the border or frontier that defined where human interaction would stop and where ecological harmony could remain. The force of exploration and evisceration of boundaries also helped to eliminate the idea of an arena where human interaction was absent. The removal of this frontier helped to create a domain where human involvement and action knew no limitations and this lack of control helped to hasten the process of environmental destruction.
I also cannot agree with this statement, although I would agree that the ecological consequences were much greater than historians admit.
Consider that the economic values and systems which Europeans brought here were based on basic capitalist greed, on exploitation of resources whether it be gold, silver, agricultural land, oil or water, not to mention human resources.
In pursuit of these resources over time, massive tracts of forest were clear cut, mountaintops removed, rivers diverted and prairie plowed and planted, while animal species like the buffalo were hunted to near extinction and population increases put pressure on other natural environments. So it's not as though this statement lacks merit.
I do not think I can agree with this statement, although it is of course a matter of personal opinion.
I think the human consequences of European exploration were bigger than that of any other single action (except for possibly the Industrial Revolution and the Holocaust). Because of European exploration, we got the near-extermination of native populations in North America and the decimation of the native populations of South and Central America. Because of European exploration, we got the African slave trade and slavery in the Americas. You can also argue that European exploration got us the United States and a worldwide move towards democracy.
To me, these effects are much greater than any ecological consequences could possibly be.