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It's done this way in real democracies... A security service or police organisation has to prove to a judge that the requested tap or eavesdropping on anyone's communications is justified and that there is probable cause for such an action. If the judge reckons the proof is inadequate, the tap or eavesdropping just doesn't happen.
And that is the way it should be done here as well... In fact, allowing unfettered eavesdropping as the ANC wants, is probably unconstitutional (so there could well be a challenge there).