One of the key debates in the history and theory of rhetoric is whether the art of rhetoric should be taught as a purely technical art without ethical considerations or whether the rhetorician has a duty to examine the ethical implications and outcomes of rhetorical teaching and activity.
Cicero is an interesting figure in this debate. He defended clients who were clearly guilty, and he was definitely ambitious and very attracted by wealth and power. But his rhetorical theorizing, administrative posts, and eventual support for the Republic demonstrated a care for ethics. Some of his philosophical works such as De Officiis, De Re Publica, and the Tuscalan Disputations shows a clear concern for philosophical ethics.
Of Cicero's rhetorical works, his youthful De Inventione is a purely technical treatise that does not discuss ethics, but De Oratore is much more philosophical and advocates a more responsible view of rhetoric. Various characters in the dialogue take different positions on the nature of oratory. Crassus and Cicero, as characters within the dialogue, both hold orators to a high standard of knowledge, responsibility, and ethics. They see oratory as fundamental to a well-governed state and feel that orators should be serious political and moral thinkers rather than simply skilled in style or expert in dazzling audiences irrespective of the truth or value of their positions.