A person can think however they want. Actions, like many have said, define a person in the end. Someone can advocate for peace with malicious intent, but they will still likely be remembered for advocating peace and not for their impure motivations. If these contradicting images are revealed to the public, that is still an act against that person, and is no longer a thought.
However, this is only from the public's view. When it comes to people, they may as well be the embodiment of their thoughts. Everything is fueled by something. The same person who seeds their own goals under the guise of peace will not think of themselves as one who acts with the intentions of bringing peace. They will be looking to call forth whatever it is that they want, and be aware that what they present to the public is not the truth.
So, both points are arguable. It depends on whether you value the individual or the community. Actions are what are remembered, and thoughts are a person's reason. Even today, this comes into relevancy because people want to know why certain figures in history did what they did. Thoughts make a person human, after all. Without thought, seperation of man and beast would be nigh impossible. Without action, man would have been left behind long ago. Both thought and action are important indeed.
In the lines from Shakespeare's "The Tragedy of Macbeth," Lady Macbeth is talking to herself while she is sleep walking. She feels so guilty that she cannot sleep properly. In that respect, she means that she and Macbeth do not need to fear anything because they are so powerful that nobody will believe they are responsible for killing Duncan. However, she does not actually think so - she is only trying to convince herself of it because she is under the impression that everybody is suspicious of Macbeth.
