In Julius Caesar, why is Cassius against letting Antony speak?
Cassius is a far better judge of character than is Brutus. Cassius knows that people sometimes have hidden agendas, real motives that lie behind their stated motives. Such people can be very convincing in their deceitfulness. (Cassius should know about hidden motives since he manipulated Brutus into the conspiracy through lying and deceit.)
Cassius does not want Antony to speak because he does not trust Antony's motives and because he understands how powerful and convincing Antony can be. Cassius also knows that the people of Rome are easily manipulated and politically fickle; they don't remain loyal to their leaders for very long. Cassius can foresee how easily Antony could turn the Roman citizenry against the conspirators. In planning Caesar's murder, Cassius wanted to kill Antony, as well. Even then, he recognized Antony as a dangerous adversary. Brutus overruled Cassius, and Antony lived. Brutus overruled Cassius again in letting Antony speak, and the conspirators are driven immediately out of Rome by the citizens Antony skillfully manipulates into an enraged, violent mob.
cassius is a good judge of human nature. he has an idea of the real nature of antony, but brutus regards antony as a frivolous young man. he wanted antony to be killed along with caesar. he did not want antony to speak at caesars funeral. he is overuled by brutus whom he loves very much. it is said that if cassius had given the orders for the battle at phillipi and the funeral and death of caesar there would have been no revolt