Because I am part of the interdependent web of all existence.
... the only way to restore balance to the ecosystem.
Let's not give the ID crowd ammunition.... we break the loop that keeps everything balanced.
The earth's ecology is a dynamic system: species emerge: species disappear; niches appear; niches disappear; existing species compete for existing niches; species displaced from vanished niches displace other species or disappear. There ain't no balance. There ain't no interdependent web of life. Life is opportunistic. Populations boom. Populations crash. Ranges expand and contract.
Why save the grizzlies? Because you will miss them when they're gone. Why save the cane toad? Got me. Mosquitoes, ticks, lice, bindweed? Got me again.
Why not prune the ecology down to people, grass, and cows? BSE, and who knows how many other headaches arising from a too limited set of metabolisms, and the metabolic enzymes breaking down proteins to be recycled. The "closed cave" ecology the Israelis(?) found? Half dozen new species --- gonna be a hundred or more before they've catalogued it completely. Truly closed? Gonna have to wait on that --- dollars to doughnuts, they're going to find an energy source percolating in with the groundwater.