The reason for the Rule of Lenity is partly to enforce the separation of powers, and partly to protect defendants from activism by requiring courts interpret the law using strict construction, and in cases of ambiguity, ruling in favor of the defendant.
However, this explanation ignores the reason for the separation of powers, which is to require that all legislation satisfy a) Naturality, b) Commonality and c) Concurrency: meaning that neither the legislature nor the courts may bypass the Natural Law (science of cooperation) nor the people.
This understanding of the causes of the separation of powers maintains the ‘scientific’ explanation of American scientific government and prohibits the treatment of the legislature as sovereign instead of the people, and the people only within the natural law of cooperation:
“Reciprocal insurance of Self-determination by self-determined means, by sovereignty in demonstrated interest and reciprocity in display word and deed, limiting us to cooperative markets for consumption, and cooperative markets (houses of government) for the production of commons, and the resolution of disputes in courts of natural, common, concurrent law.”