The first part is about the subjectivity of good and bad. (Almost) nothing is either universally good or universally bad. The vast majority of things are good for some and bad for others. (For example: If deforestation was bad for everyone, no one would be doing it, but there are people who profit off of it and some, sadly, whose livelihood depends on it)
That’s (partly) why it is false to just say “everything that is natural is good, everything that isn’t is bad”.
(That was my response to jhbratton saying that if humans were a part of nature and all we do is natural, that would be an excuse for us destroying the environment. It isn’t.)
As for why I believe that humans destroying the environment is natural (but, again, neither ethical, nor “good”), I didn’t explain, as I didn’t want my reply to be so long. But pmeisenheimer put it very elegantly and much better than I could have: