[Shacklet0n]

Others haven't already pointed out that you're mistaken regarding "an insanely large portion of the CO2 is simply us and our livestock breathing." But also, consider this:

The carbon in the CO2 that you breath out comes from the carbon that you consume. That carbon - by virtue of its state - is part of an equilibrium carbon cycle that makes our planet habitable. I.e. the apple tree consumed CO2 from the atmosphere to create the apple that you ate, and you returned back to the atmosphere the carbon that the tree previously consumed.

Now consider the carbon that has been isolated from the cycle over billions of years as the planet became habitable to creatures such as ourselves and our non-human friends. That carbon is in the form of coal, oil, etc. If we leave that stuff in the ground we retain the current carbon equilibrium. If we burn it, we change the equilibrium by taking sequestered carbon from the ground that was "locked away" and add it to the atmospheric carbon cycle.