Traffic volume for binaries is higher than that of text because the message size is larger. They are also often chunked into sub-messages that Usenet servers counted as individual messages but semantically are not. Many binaries are legitimate redistribution, although of course not all.
Do you mean to say that there are more binary messages than text messages by an order of magnitude before chunking and that none of those binaries were permitted copies under the law? Because I'm going to need to see evidence to be convinced of that.
And the history of Usenet also shows that people do think that the fact that something is mis-used should preclude any use of it. One can look to the history of how several organizations discontinued their Usenet services as a lesson for that, too.