Brutus is unethical, because he betrays his country and the man who loved him.
This is an interesting collection of traits you have here. First of all, Brutus definitely goes through a progression throughout the play. The Brutus that we see in the beginning of the play and the one we see at the end of the play are not the same man. He is an evolving, dynamic character.
Brutus was a man of principles. He was drawn into the conspiracy by others, remember, he was not the one who started it. Actually, in many ways Brutus was a coward. He stabbed last not because he wanted the bloodthirsty final thrust, but because he was horrified at his betrayal. Remember, he and Caesar were close. He loved Caesar once. Caesar was a father figure to him. Brutus has to talk himself into his actions. He has to moralize and legitimize the conspiracy's actions at every turn.
I would say that Brutus is an honest man, if not an honorable one. For instance, he flat out tells the audience that he does not think that Caesar has done anything yet worth killing him for, but they are making a pre-emptive strike against him.
Brutus is honest here not just with himself, but with the audience in this soliloquy. He is telling himself that he knows they are about to kill a man not for what he has done, but for what he might do. He says that “lowliness is young ambition's ladder” and that basically means that Caesar is going to claw his way to the top. Therefore, Brutus and his minions must think of him as a “serpent’s egg,” not harmful yet, but harmful when he is hatched, and “kill him in the shell.”
You can tell the truth about what you are doing if you believe it is right. Brutus is honest about what he is doing, as horrible as it is. He comes right out and tells the people that he killed Caesar. He even still has the bloody knives and they hold them up and run through the streets with them shouting. Remember, they think they are liberators. There is no reason to hide.
Second, is Brutus manipulative? Definitely so. He is manipulated, of course, into joining the conspiracy, but look at this speech! Look at how he is playing with the audience. Okay, granted, normally we do not talk to people who are not there. This is a play though. So let’s take actual realistic examples. Look at how he controls the people in his group. Every time Cassius makes a suggestion, Brutus shifts the power back to himself. This is the man who started the conspiracy, or at least had control of it when Brutus joined.
A good example of this is the argument over whether or not to kill Antony. It is actually a well-reasoned one. Brutus should have listened to Cassius. Instead, he makes eloquent speeches full of platitudes.
Our course will seem too bloody, Caius Cassius,
To cut the head off and then hack the limbs,
Like wrath in death and envy afterwards;
For Antony is but a limb of Caesar:
Let us be sacrificers, but not butchers, Caius. (Act 2, Scene 1)
Brutus also manipulates the people during his speech to them when he tries to convince them that killing Caesar was justified.
Both of these are also demonstrating trait number three in the list of character traits. Brutus is idealistic. He did not want to kill Antony because he thought that they could get away with their coup by only killing Caesar. He was also idealistic enough to think that Antony would be no danger to them. He thought that the people would blindly follow Brutus and his men as tyrant killers and liberators. That is absolute nonsense. The people were confused and frightened. Caesar had the base, not Brutus. Antony was Caesar’s loyal follower, so they followed Antony. All he had to do was produce Caesar's will. Brutus didn’t even have a chance.
What Brutus was not was ethical. It is not ethical to kill a leader because you think you can be a better one. There is a way to eliminate a leader. It is called the rule of law. Rome had a system of elections, normally, in which the consuls were elected every year. Caesar was elected and was supposed to be consul one year, and then was named dictator for life by the senate. The senate gave him the honor, they could take it away. All of Caesar’s honors were given legally. Brutus and his men were just upset that Caesar was so popular. He represented a threat to their power and they did not like it.
Caesar did refuse the crown that Antony offered him.
Historians have argued and debated about the incident when Caesar refused Antony’s crown, and the true meaning behind it. However, whatever the reason that Antony offered it, or Caesar refused it, the truth lies here: Caesar refused it. He was also very angry when anyone called him king. These are facts. Caesar did love his country and did not want to be king. What Brutus and his men did was wrong. This is why the people did not follow him.
Brutus is in some ways a tragic figure, at least the way Shakespeare portrays him. He wants to do what is best for his country, the way that he sees it. He buys his own message. He twists his ideology into believing that he is right, and will not listen to anyone's advice but his own. In this way, he makes all the wrong decisions, and pays the ultimate price.