One thing about a binary - an on and off system - is that it does facilitate control. It acts as a lever. If you have two options for something to take that you are trying to control, it is easier to make those options distinct, and depending on the outcome you prefer, encourage a certain direction for whatever is subjected to that binary.
The simple binary of life and death is significant to whatever pocket of energy is organized and "living." And so the life side of the coin must be focused and deepened, and the death side of the coin, pushed away and curtailed.
Socially, having two options - such as good and evil - allows one to take one position or the other, which leads to more stark and decisive actions. On the flip side, it also allows those with power to quarantine one or the other designation, and then use that designation as a weapon, while retaining its binary opposite as a shield. Having even a third option - let alone a spectrum of options - makes things a little more unpredictable and a little more complex, which is much more difficult to manage.
One of the peculiarities of this industrial civilization, and probably all civilizations, is that as an entity it is incomprehensibly complex, but what makes it work, or what makes it persist in its current state, is a complexity that is made up of simplified binaries stacked and stacked upon each other.
Because a binary allows a given aspect of civilization to take the shape that is desired. And a binary has to be maintained. Its boundaries and its functioning need perpetual stewards.
