Question

Why did decius tell marcus brutus not to allow antony to speak at caesar's funeral?

Answer 1

this was because Antony was a good speaker or orator and decius tell Marcus not to allow Antony to speak at Caesar's funeral because he said that Antony may create a rebellion among the mob by speaking in funeral Caesar's funeral

Answer 2

cassius tells the brutus not to allow antony to speak at caesar's funeral because he feared that antony would use his superb oratorical skills to sway the masses against the conspirators  and undo all their plans .