You're half right. Corporations are just made of people. But, they're more than the sum of their parts. The numbers and complexity do more than provide anonymity: they provide a mechanism where individuals can work in concert to accomplish bad things in the aggregate, without (necessarily) requiring any particular individual to violate their conscience. It just happens through the power of incentives and specialization. If you're in upper management, the complexity also makes it easier to turn a blind eye to what is happening down below.