What is the main rationale that brutus gives in his act 2.1 soliloquy

You didn’t share any options to choose, but I have found some statements and I guess the right one must be ‘’Caesar will become a tyrant because Caesar is already a tyrant.’’ Brutus has a cruel plan on Caesar and even though he is the one of the closest persons to Caesar, he commits conspiracy and wants Caesar to die in order to dispense justice for the common good.