Do you know what all those megafauna, jungles, and forests had in common? They rely on or emit. Oxygen originated with cyanobacteria. [1] When cyanobacteria emerged they basically just genocided the entire planet because their emitted oxygen was extremely toxic to most of everything else alive at the time. It'd be like if plants today started emitting gaseous arsenic and flooded the oceans and atmosphere with it. So you end up having your enlightened aliens longing for a planet that exists only because of 'pollution' on a scale that caused a mass extinction event. We should work, within reason to preserve what we have, but the self loathing is nonsensical.

Humanity isn't perfect but it's pretty awesome, and may ultimately be the only reason that the species that exist on this planet are able to continue to exist. We're overdue for another major external mass extinction event, but this time humanity will hopefully be able to mitigate its effects. And as we expand our reach into the cosmos we'll certainly be bringing along our furry friends, tasty friends, helpful bacteria, and many others along for the ride. And they'll continue to thrive far beyond what might otherwise be their fate, left to their own devices on Earth.

If anything I'd think our enlightened aliens would be worried about us managing to kill ourselves before we reach into the stars. We're probably quite close, on both accounts. Hopefully we win the right race.

[1] - https://en.wikipedia.org/wiki/Cyanobacteria