the problem is overpopulation, given the room, humans don't tend to cause as much trouble, but with anything, the added complexity and added entropy of a structured OVERpopulated environment, and that's where things breakdown, have problems, and we end up cannibalizing our own environment, populous, water sources, air sources, ect, ect.
the earth can only really support about 4-5 billion people
past that?
well?
Just look around and see what we are doing.
chopping trees down and covering the earth with asphalt and cement...sucking all the hydrocarbon out of the earth as we can, whilst blasting much of it into the groundwater in the process.. and the rest of it into the air after we burn it and add co2 into the air also.
polluting everything we see, with chemicals, radioactivity, natural pollution (sewage, like India, etc)
the air, the ground, the water, even the area in space, around the earth is RIDDLED with space-garbage...
It's rather scary, and people look the other way, and continue to do so.
when it'd dire we do something, but the problem is, the "something" we must do, is HALF the damn earth's populous.
so that's kinda a hard sell, no?