Because it never stops. It's a gigantic dragnet of everyone and everything. Sure, a huge majority of it is blah blah blah about how Sally is tired of putting up with Tom's crap and Judy's going to have a baby...
Where it becomes an issue is: you can find out anything you want to know about someone by who they talk to. Are they part of a union, are they part of a certain political/religious group, are they having an affair, did they talk to someone 2 months ago that went on a shooting rampage today....?
The entire purpose is to dig up dirt on people, and I don't trust anyone in the government to hold and use that information properly, professionally, competently, or ethically. It is a very dangerous tool that they have, and anyone who thinks it will only be used against "terrorists" is incredibly naive.