Working in the infosec world, I know that if you establish defense in depth through controls on a variety of levels, a security program can fight off a lot of attacks you never even know about. So, purely in that vein, for cases where components of the Patriot Act worked, we really will never know what we avoided. That said, that's not a concept to justify a blank check and a "forever" theft of liberties.
Similarly, I think the "we don't have documented evidence of violations of civil liberties is a terrible argument." If the NSA has illegally overheard one of my calls or illegally read any electronic correspondence, then my rights have been violated, whether that led to direct harm to me or not. I don't know that it was a violation of my civil liberties per se, I did land on a no-fly watch list for awhile. I couldn't check in ahead of time, I got the pat-down every time through security, I got secondary screening at the gate. I spent 2 months going through some arbitrary TSA process where I had to submit a bunch of information and hope they didn't decide that I was an international menace. In the end, I got a letter saying something along the lines of, "We can't tell you if you were on a list, we can't tell you why you were there if you were. We have reviewed the information you provided and have come to a final resolution on the matter. We cannot tell you what the resolution of this matter is and you cannot appeal the decision. Here is your Redress Number to be used on future travel reservations." My suspicion (partially confirmed by a gate agent that was probably subsequently fired) is that someone with the same name landed on the list, so they were treating everyone (same birth date or not) with the same name as if they were that person. This was almost 5 years ago and to this day, if I forget to add the Redress Number when I make a reservation, I get all the added security checks and scrutiny.
I really don't think either statement is particularly strong.