Think about this: Everything has a purpose.
Mosquitoes suck blood, bats eat mosquitoes, bats get protein from blood in mosquitoes. Without mosquitoes, bats attack larger prey, probably could become carnivorous.
Bees transfer flower pollen, which allows more flowers to grow.
Mice eat berries and nuts, snakes eat mice. Mice diet means snake doesn't eat fruit/nuts.
But humans are at the very top, we can consume nearly anything, and as a whole, are virtually indestructible.
The balance is what humanity decides it is.
http://www.cracked.com/article_17481_p2.html