It's nothing of the sort. If the stated purpose is the electronic surveillance of al Qaeda operatives what is the consequence of getting that wrong (as in intruding on an innocent conversation)?
If you have to ask the question then you need to look at your value system.
Certainly you have more confidence in your position than to resort to this, don't you?
It's basically the same question, as what's the harm in convicting an innocent person or what's the harm of getting a bad tip and searching the wrong house. The freedom from the arbitrary use of government is a basic human right and we have a system which is intended to protect us from such intrustions. If you don't believe in basic human rights, there's little I can do to convince you of their necessity.