It is so unfortunate, and to my mind a sign of the ummah's decline, that not one of these organizations asked Kabbani for the evidence or information that led him to make his statements. This is usually done when one is concerned with pursuit of truth, when one strives to find excuses for their Muslim brothers and sisters, and when one attempts to verify stories-- all of which, to my understanding, are Muslim behaviors.
It is also unfortunate that it appears none of the signatories checked the accusation against the text of the speech, in that there are clear inaccuracies and manipulation of meaning.
I am not a part of Kabbani's group, nor am I necessarily defending Kabbani's statement. But it has been clear there are people who are "out to get" Kabbani-- not just disagreement, not just question, but seem bent on destroying the guy and will manipulate to do it. Not too long ago we also saw accusations regarding Kabbani's finances and lifestyle, but again, no real effort to pursue truth.
The only question Kabbani needs asked--- and before any distancing, condemnation or attack-- is "on what basis and on what evidence do you say the things you say?"
Did anyone bother to do that?
It appears to me the answer to that question is "no".
In which case, I must say, to my best understanding, not one of the signatories behaved in a manner consistent with what I understand to be standard Muslim practice in such a situation.
Allahu alim, of course