Cao Cao is a villain, lean in troubled times, but he is very sincere. Talented people won't betray him because he was unfaithful to the Han Dynasty, such as Guo Jia and Xun. They are all outstanding wizards, because at least he never denies his treachery, so they are persuasive.
Comparatively speaking, I think real villains are much better than those hypocritical hypocrites.
The potential harm is the greatest.