I feel that one reason society pressures us to avoid crying is because of the primal power it conveys. Hearing or seeing someone else cry elicits a visceral from us, as though that fundamental form of communication from another calls to that same desire to cry that hovers beneath our socially acceptable façade. Perhaps that is why some people react to crying in anger, as they fear to have their own crying released.
Sometimes there are no words to express the welling of emotions within us. Why do we deny ourselves this outlet? Maybe we fear to face the true reasons behind why we want to cry.