Does an orator have to be morally good?

I disagree with the Greeks’ belief that an orator has to be morally good to be a good public speaker. A message may be bolstered by its truth and goodness, but history is full of examples of great orators who used their powers of persuasion for evil purposes. Adolf Hitler is a primary example of someone who was very effective at public communication, but morally corrupt. He was able to use rhetoric, symbolism and propaganda to rally an entire nation to an evil purpose. His ability to persuade so many people to follow his cause is perhaps more impressive given that the cause was based on principles that are not true or morally good. Rather, he had to overcome truth and morality in persuading others to follow him. If a message is based on truth and morality, it should be easier to communicate and require less skill as an orator. A message based on falsehoods and immorality, on the other hand, may require greater skills of persuasion, and even manipulation, in order to convince others that it should be followed. Based on an example of Hitler and his ability to persuade I think an orator should be morally good to send the right message to the society.