Brutus is blameless because he killed an authoritarian, Caesar, who was only poisonous to Rome. Brutus had no other option but to do the utmost for the citizens of Rome. Caesar would have possessed all of Rome and enslaved all the people who loved adored and admired him.
Caesar broke two laws; he crossed the Rubicon with his troops and started a ferocious war in Gaul. Caesar crossed the Rubicon with his army dressed in their war colors, which was against the law. He crossed the Rubicon because he knew that a death sentence awaited him there.(Ancientrome.biz/Julius-Caesar-bio) He was told to cross it by himself, but he was aware that he would be killed so he brought his troops with him. Caesar started an illegal war in Gaul because he wanted more money and to control Gaul. Caesar was not allowed to start a war in Gaul because Gaul was an ally.
When Caesar was asked to give up dictatorship he responded by saying that he would only do what was asked if he was consul of Rome.(Shakespeare, Julius Caesar)He did not care about the people of Rome and that they depended on him. All he cared about was controlling as many countries as he could and getting richer by the second.
Caesar's actions led to Pompey's assassination. Even though Caesar did not physically kill Pompey, he chased him and made him flee.Caesar wanted to kill Pompey because he betrayed Caesar. Caesar gave Pompey his daughter's,Julia's, hand in marriage.(Shakespeare, Julius Caesar) Pompey turned against Caesar and married the daughter of one of Caesar's greatest enemies. Since Pompey was consul of Rome he wanted Caesar to give up pro-consulship and return to Rome where he will be tried for treason. Caesar took this as a declaration of war. Caesar defeated Pompey's troops,but he wanted to kill Pomey himself. Caesar was making Pompey run away with fear. Pompey fled to Egypt where he was beheaded by King Ptolomy's friend.
Even though Caesar was a good friend to Brutus, he did the right thing by betraying Caesar. Brutus knew that Caesar's actions were wrongful;he would would not allow himself to take the path that Caesar chose. Brutus knew that he had to stand up for himself and Rome. The people loved Caesar but if they found out what kind of selfish, cruel and stubborn person Caesar was like, they would have turned against Brutus, too. Brutus did not want Caesar to have everybody overruled and under his control. Brutus stopped Caesar's plan. Any sane and kind-hearted person would have done the same if they were in Brutus' position.