Meh, cities are quite small. Their expansion can lead to eg draining marshes and wetlands (especially coastal cities), but in many places in the developed world

Meh, cities are quite small. Their expansion can lead to eg draining marshes and wetlands (especially coastal cities), but in many places in the developed world, that happened long ago. If you care about ecological collapse, you should be worried about intensive agricultural practices and agriculture in general. I think one should always be wary with topics like climate change or ecology that issues may exist at many orders of magnitude and it is important to focus on the bigger issues. (Yes there are very small areas to which some species are endemic but general hand waving about density is not sufficient for them: a farm is not dense)