Earlier quoted context omitted.
The environment is a complex web of interdependent relationships between species and ecological processes. You remove enough relationships and it'll just collapse.
That's very vague. Collapse how? According to other comments we have already remove 60% of species, why wasn't that enough to cause a collapse. Other species take up the slack left by those removed.
Say plankton dies off, say animals eating plankton die, say humans eating those animals now have less food. Say all the fish die and we are reduced to land-based food. Now we have more space competing for farm land, we have to clear forest. Clearing adds to CO2 emissions, construction, more emissions, less CO2 being taken out. It's clear how this is all one giant feedback loop. Less biodiversity, more overabundance of something else, which leads to less consumption of something else which leads to collapse of ecosystems which leads to use trying to patch things up and doing even more harm.
Just zoom out and think about things that consume things and how that loops back directly to humans, environment, overproduction, overuse and eventually unsustainable usage of resources until there are none left.