Speculative, rationalistic systems reject revelation and base the weight of their support upon the conceptions of the human mind. Therefore, their limitations should be obvious at once. Therefore, their limitations should be obvious at once. Morality results from objective reasoning that determines whether a given thing is either inherently good for the conscious human organism or inherently bad for the conscious human organism. A truly complete rational system automatically takes into account the universal interconnecting relationships between all humans in their social organism to arrive at mutually beneficial ethical decisions.
Rationalist systems are all man-centered.
God is banished from his universe and has no right to tell his creations what to do. That sounds like a Good Thing to me. All human ethical systems are willful rebellion against the Almighty God. This is redundant. Again, one cannot rebel against something whose existence is questionable or irrelevant.