Brutus is a champion of the people; his ancestors fought for democracy. He feels a ethical obligation to protect the republic from any form of tyranny. This is the main reason why he goes against Caesar. He tells the people it was not that he "loved Caesar less, but that he loved Rome more." He continues by suggesting that Caesar would have made them all slaves. "Had you rather Caesar were living and die all slaves, than that Caesar were dead, to live all free men?" He feels that Caesar's main ambition was to have complete political/martial control of Rome. He tells the people that Caesar suffered "death for his
ambition." He honestly believes that he has served his ancestors and the people of Rome by killing Caesar. He believes this so much he even tells the people to kill him if he becomes too ambitious for power. "I have the same dagger for myself,
when it shall please my country to need my death."
Brutus is a somewhat "philosophical" character. He is generally regarded as a good, perhaps noble, man deeply in love with the concepts of freedom and republican government. He kills Caesar not because he does not love him, but because he loved freedom more. As Anthony says:
This was the noblest Roman of them all:
All the conspirators, save only he
Did that they did in envy of great Caesar,
He, only in a general honest thought
And common good to all, made one of them.
His life was gentle, and the elements
So mix'd him that Nature might stand up
And say to all the world: "This was a man!"
There was no envy in Brutus, no evil in Brutus. If he had a fault it was his idealism that could not compromise with the idea of a Caesar as dictator. It is up to you as reader to decide whether there are any other factors "clouding" his judgment.