Slander and libel is not acceptable but, not being a legal expert, I cannot comment on whether such an act was committed.

You do not need to be a legal expert to recognise an unsubstantiated accusation.
If I am accused of beating my wife or mistreating my dog, how can I "robustly disprove the allegation amongst your peers?"

If Mudcat does allow unsubstantiated allegations, we at least can show our own disapproval of such behaviour.
I have and I do.
Will you join me when it next happens Dave?