Because you can detain a person without trial, without time limit, to answer question to which they could not possibly know the answer, and punish them for not knowing.

It's something of a frustrating issue.

It's something of a frustrating issue. The public thinks not enough is being accomplished. I don't know if we'll ever be able to declare it clean.

Now many might not agree with that decision but it was a decision which demonstrated a considered approach.