A'isha
Miss Schoolteacher
No, you're completely wrong on every point. They didn't argue that he didn't call for her firing. Why would they, when Sherrod didn't claim that he did? He argued for dismissal on grounds that I haven't even mentioned (so the court ruling has no bearing), and even if she wins (which she hasn't), libel and slander are still just speech.
No, they're not "just speech" that his political opponents don't like (which is the part of your argument that I'm addressing, not the "calling for her firing" part). They're actionable offenses, meaning that Breitbart would be (depending on the outcome of the suit) responsible both legally and monetarily for his role in what happened to Shirley Sherrod.
In fact, these types of lawsuits are precisely because people like Breitbart try to avoid the responsibility for the deliberate and intentional harm caused by their statements by hiding behind the "hey, it's just words, don't we have free speech in this country?" defense.