The simple thing here is Cao Cao is the bastard character used for teaching every generation of people to distinguish between good guys and bad guys. In Chinese 分辨忠奸。 You are entitled to your own opinions, you are not going to convince most people that this bastard is one character that had won respect or trust or be any positive role model for most people. You can go and try.... I am not going to stop you. In the same era as CaoCao there were very respectable characters set as positive role models for children to learn from e.g. 关云长。 Together with the vicious CaoCao the righteous characters produced contrast and set positive vs negative role models serving the purpose of education.