Unfortunately surveillance NSA-style is very often of the take-no-prisoners type. They collect it all and then search for key words and phrases. You cannot get a warrant against a single target for this type of surveillance because you looking at the full database of all the calls. Assuming that they find something of interest they look a little closer. There could easily be hundreds of thousands of such events every month (I'm guessing). Look harder and cut these down to a few thousand. Look harder and get them down to a hundred or less and off you go to the FISA court to get your warrants. If you kill the program at the top you will kill it at the bottom.
exactly. it's impossible to get a warrant for every piece of information "harvested".