Exploitation has an ugly sound to it, and while it's true that any government has to do something to that effect in order to function in itself, it should not be misconstrued that said exploitation is necessarily of a malicious kind, but rather a necessary one.
In answer to the question about comparison, even if we take Liu Pei as himself, without comparing him to Sün Ch'uan or Ts'ao Ts'ao, then yes, he still cares for his people. Obviously the novel emphasizes this, but it's quite prevalent even in historical accounts. His empathy, his caring for the common person is evident, so yes, you can say he has a parental love for his people, not so potent as a father and mother to a child might be, but that is understandable. It's a little harder to take care of a family of five thousand than it is five.
And certainly times have changed. We are raised with less and less ethical standards by which to hold ourselves, which I think is a large mistake on our society's part. I am only something of a good man because my Grandparents and Parents provided me with a model by which to live up to. Without that, I would be self-serving and very little but, for I know myself at least that well. This same observation can be applied to a man like Liu Pei, who held himself to a standard of ethics, whereas Ts'ao Ts'ao did not, and Sün Ch'uan did only in a mechanical fashion, rather than a truly conscious one.
To say in simpler terms; Liu Pei followed ethics by his own will. Sün Ch'uan followed ethics out of tradition and was thus swayed by greed. Ts'ao Ts'ao ignored ethics because of his own greed.