There are no limits, natural or otherwise, to corporations' potential size. Because of their political power, they are able to define or at very least substantially affect, the civil and criminal regulations that define the boundaries of permissible behavior. Virtually no individual criminal has such abilities. Corporations can combine with each other, into bigger and more powerful entities. These unique attributes give corporations extraordinary power, and makes the challenge of checking their power all the more difficult.
Corporations have no conscience, or has been famously said, no soul.
As a result, they exercise little self-restraint. The fact that corporations are not like us, their very unique characteristics, makes crucially important the development of an array of controls on corporations. And there is the imperative of directly confronting the corporate claim to personhood and community neighbor status - both in the law and in the broader culture. This is the beginning of a sketch of an ambitious agenda, but there is no alternative, if democracy is to be rescued from the corporate hijackers who masquerade as everyday citizens.