Why does Brutus disagree about taking an oath?

In William Shakespeare's "Julius Caesar," Brutus objects to the taking of an oath because he feels that honorable men engaged in a just cause should be trusted at their word. This plays into Shakespeare's development of the Brutus character as a strong and noble man.

Brutus expresses agreement with his fellows that, although Caesar is a good man, the power of the crown might change his character. When Brutus joins in their conspiracy to assassinate Caesar, it is proposed that the group seal their pact with an oath. This is when Brutus speaks his objection to asking an oath of honorable men. Whether Brutus displayed hubris or a sense of honor is left to the reader's point of view.