It takes considerable confidence to stand at the front of a lecture hall with 150 sets of eyes staring at you and present yourself as an expert on a subject. Are all instructors egotistical, or could they be experts willing to impart their knowledge? I've met my share of lawyers as well, and ego was not the personality quality that I saw. In fact, most prosecutors I know have internalized the pain and suffering of the victims of crime. They dream about, drink to forget about it, and sometimes do extreme things to clear their heads of the ugliness they encounter. Pretrial evidence reduces them to tears, they are sleepless throughout the trials, and preparing closing arguments is a bit like a brain splat where they want to ensure that they've covered every angle that the defense presented. Many prosecutors are damaged people by the end of their careers, having been consumed by their years of service.
I can see that those who are unhappy with the jury decision to find Knox and Sollecito guilty want to blame someone, and that they have chosen to blame only one of the prosecutors rather than both of them or the jury, but I would be reluctant to jump to the generalization that all lawyers or prosecutors are egotistical maniacs that want to win at all cost. If people disagree with the jury's verdict, then disagree with it ... don't blame one of the prosecutors that presented the case, and don't paint all lawyers as egotistical maniacs that would find joy in convicting the innocent if only for the sake of winning. That's the stuff of books, not life.