The citizens of Rome are deeply affected by the rhetoric of Marc Antony. Consequently, they are moved when he casts aspersions upon the credibility of the "honorable" Brutus and his claim that he loves Rome more than he loved the purported tyrant Julius Caesar as he has led them to believe. So, they begin to believe Marc Antony, who suggests that the conspirators killed Caesar so they could gain power.
Because of Caesar's great conquests, the Romans have held their leader in esteem; furthermore, they are not so aware of Caesar's private desires for power as the noblemen. Thus, after the assassination, when Brutus explains that Caesar "was ambitious" and would become tyrannical, he assumes that there is no man who "would be a bondman [slave]" if he does not have to be. He concludes his address to the Romans,
BRUTUS. Who is here so vile, that will not love his country? If any speak; for him have I offended. I pause for a reply.
ALL. None, Brutus, none! (3.2.30-32)
However, after the clever Marc Antony creates doubt in the Romans' minds by means of the effective repetition of "honorable" and "ambitious" as well as other rhetorical devices such as antitrosphe, he creates doubt in the minds of the plebeians, especially when he informs them that Caesar filled the general coffers and willed the citizens money. His ironic remarks,
Ambition should be made of sterner stuff
Yet Brutus says he was ambitious;
And Brutus is an honorable man. (3.2.91-93)
effectively stir one plebeian to remark, "Methinks there is much reason in his sayings" (3.2.107). Further, others are stirred as Antony continues and reads Caesar's will, and when he insinuates that Cassius was envious and Brutus treasonous, the Roman plebeians are incited to burn the house of Brutus and to "revenge his [Caesar's] death!" In fact, a riot ensues, the beginning of a civil war.
After Marc Antony brings the conspirators' honor into question, the plebeians clearly question their integrity and the credibility of Brutus.