I have noticed many arguments being criticized on debate.Org simply for "not having sources". Aren't some arguments valid based on other assumptions that generally exist in a society, such as that the earth is round? This is not to say that it is wrong to question those assumptions, one should question everything, but at what point does a need for citations merely become an appeal for authourity and not a valid criticism of a valid argument?
Citations are necessary in some debates, but not in others. For example is you are debating quantum mechanics citations are a benefit as they can help the readers understand finer points of the argument which are not relevant to the debate but are relevant to understanding the argument. In some philosophical debates citations are not always necessary as they rely on reasoning.
Let me just add that if someones logical reasoning's are getting used to promote a flawed theory (like creationism) then citations are necessary.