"Given that we sit atop the food chain, nothing preys on us so there's nothing to stop our growth."
This is simply a major fallacy of our very ecologically fallacious culture. There is NO ‘top' to the food chain!
In fact, evolutionary tendency is from carnivorous to omnivorous where we see some plant eating capabilities, to exclusive plant eating capabilities and then further specialization (such as the bovine specialized stomach) adding an ability to digest much more commonly available foodstuffs, grasses.
If one looks with an accurate ecological lens, one sees that ecology itself moves towards dietary specializations that can support great herds, meaning larger and larger population numbers... and it turns out, these greater numbers are necessary to a number of other specialized ecological functions including soil conditioning.
The assumptions regarding human behavior and our place in the evolutionary history of the earth's biosphere (that are so often repeated) are simply wrong. I do not care if these are assumed and repeated by professors of environmental science, they are still absolutely wrong and born of culturally induced assumption and not accurate science based upon an acquaintance with nature.
Humans are herbivores: http://www.goveg.com/naturalhumandiet_physiology.asp
Furthermore, had all of us not been reared in a elitist dominator culture, we would NEVER have thought to fish! Over-fishing depends to the notion that fish is an appropriate food for humans, which it is not! And has only been promulgated by cultures and vestiges of vanquished cultures that taught an errant hierarchical model for social organization, the purpose of which was fundamentally to justify rule by an elite class supported by a violence-enabled class, the warrior cult.
So, ALL meat-eating and the myths that support it (in human societies around the world), stem from the ‘corporate/military' (temple-based) model for society.
Is it any wonder that we have adopted a (completely non-scientific) cultural fallacy such as ‘top of the food chain'?
The door out of the insanity (killing spree) is to decide to participate (ecologically speaking), because our attempts to dominate nature are being answered with a ‘no thank you' from the rest of life.