I'm not sure how others feel, but for me the systematic nature and the scope of collection are what get my hackles up. Requesting specific information on a specific individual because of the suspicion that a crime has been committed is perfectly reasonable. Collecting information on everyone in order to search for illegal activity feels like a serious violation of privacy. We can debate about the kind of information they can get through NSLs only being "metadata", etc., but that's the crux of the issue for me.