Assuming the natural resources you might want to exploit are living beings, you have to maintain an equilibrium in the environment or you can get resource starvation, which then impacts you directly, either as increased costs or an end to the goods entirely. You can easily see this in things like elephant/rhino poaching, where the unregulated demand will eventually result in no more supply at all. Even slavery requires considering the costs of maintaining the slaves, as if the slaves deteriorate, they won't be as productive, and it will cost you more to acquire new ones. Or if you attempt to take over some new lands, but your diseases wipe out the native population, now you don't have the natives to use as slaves anymore.
In respect to the American economy today, inequality and exploitation can lead to several problems. 1) Lack of skilled workers, 2) ballooning health care prices and increased taxes, 3) political unrest leading to trade problems, not to mention limited business growth, 4) overthrow of government, 5) state taking over commercial entities, 6) economic collapse , 7) massive refugee crisis. Oh wait, that's Venezuela. For us it's just the first few.
No matter what, you will eventually have to consider the costs to others if you want to acquire unlimited resources.