Are there any kinds of acceptable ambitions, or are we all just supposed to be content with our lots, whether we're kings or servants?

If we didn't have ambitions, there would be a lot of unfulfilled people in the world. Ambitions are dangerous when a person goes after his/her dream at the expense of all others..... like Macbeth. Macbeth was willing to take on the murder of another human being..... that's not the same thing as a doctor's desire to become the head of his/her own department.