There can never be enough rules to cover everything we recognize as an ethical situation. Due to the complexity of life, the promulgation of rules as the entirety of the ethical dimension can encourage an exception or loophole mentality ethics becomes manipulation.
Rules can conflict.
All rules need interpretation. We really cannot do without some rules. Everyone has them no matter what. Rules are essential for understanding the difference between right and wrong the main parameters of what is expected of everyone. Thus they coordinate human behavior in a rough and ready way.