Many people have taken offense at the behavior of the defendants' families. That doesn't mean their behavior has been offensive. As Kaosium put it, the families can't make a case for their children's innocence without defying the prosecutor and the police. Amanda and Raffaele would sit in prison for the next quarter century if no one were allowed to say anything that might be interpreted as offensive by those who would impede others' freedom to speak.
So the same, people here may take offense from what John Kercher says, because he says Amanda is guilty, and states he believes she is guilty.
But you have stated that John Kercher was in offensive mode and the Knox were not, wording the phrase as meaning that objectively Kercher was attacking and the Knox did not attack. You did not just say that you
took offense from his words. While we could perfectly agree in the same logic saying "Amanda is guilty" may be not an offensive comment, it is meant to say that's what she is, and Kercher stating he thinks Amanda is unequivocally culpable of the killing of his child is stating a fact: this is what he believes.
Though, you stated that in youropinion is an "offensive move" (meaning objectively offensive) , and instead the Knox moves are (objectively) all respectful, it is just other people - like the Kerechers - who
take offense of inoffensive statement.
I'm not sure the Knox, Mellas and Sollecito families can be said to be at fault as long as they have never said anything attacking, criticizing or even questioning John Kercher's child.
I am sure John Kercher can't be said to be having a offensive strategy in contrast to the Knox strategy on the media, in the same logic.
When you note "the families can't make a case for their children's innocence without defying the prosecutor and the police", you could just
1) try be more detailed on the verb "to defy" (which is not the same as
to accuse)
2) focus on the difference between making a point in court and making a case in media.
You are not able to spot these differences, instead you will support a line that goes on trying to make a case in media because self-defeating in court, and while performing this dirty trick, projects this very blame on others: police, prosecutor, judges, experts, Kercher party, witnesses, etc.
In italy we call this game
ciccio mi tocca.
"I am here on tv because I want to use the media, rather the court, to accuse these people of being corrupt and dirty. Their blame, which proves they are corrupt and dirty, is they (maybe, could, allegedly, in this irrelevant points) have used the media, rather than the court, to accuse..."