In living memory, "rule of law" has included the holocaust, gulags, forced sterilization of the handicapped, forced abortion, police brutality directed against minorities, and various other forms of tyranny and injustice. Many times those things are described by the government as "in the best interests of the people".
Those are the associations some people have with the line "limiting human behavior". Of course that's a rather one-sided presentation -- I've left out positive things like "ending slavery" -- but the point is to demonstrate where the fear comes from.