Oooh! Great question. While I think careful readers of this play could adequately argue for either one of these choices, I believe the greatest point of tension is not Caesar's death (which happens relatively early on and the play is not the play without the consequences of Brutus' decision to allow Antony to live and to speak at the funeral), but Brutus' veto of Cassius' concerns regarding Antony's threat to the conspirators. Brutus is not the judge of character that Caesar is. He sees all people for the good in them...with the exception of Caesar's greed and ambition, the reason Brutus chose to join the conspirators.
Antony follows Brutus' boundaries for speaking at the funeral to a "T". He speaks well of Caesar, and does not speak "ill" of the conspirators, although he repeats, with a different tone of voice, how "honorable" Brutus and the others are. This repetition drives home that they are NOT honorable, but traitors to the state and butchers to Caesar. All events unfold accordingly.