Why does brutus feel that he must kill Caesar immediately?

Brutus feels compelled to kill Caesar immediately because he believes that Caesar's ambition poses a direct threat to the Republic's democratic ideals and the freedom of the Roman people. He fears that if Caesar is crowned king, it would lead to tyranny and the erosion of the values that Rome stands for. Brutus is torn between his love for Caesar and his duty to protect the Republic, leading him to conclude that the act of murder is a necessary sacrifice for the greater good. His decision is rooted in a sense of honor and a commitment to what he perceives as the welfare of the state.