To take just one type of harm done by NSA surveillance, look at parallel construction. The NSA has been (unlawfully) handing over intel to the DEA. The agencies have been trying to hide this use of NSA data, likely because it's illegal, an abuse of an already questionable surveillance program, clearly unconstitutional, and destroys the basic premise of Amercian law (defendants are allowed to confront their accusers in court). While we don't know how many people have been unjustly charged and imprisoned, senior DEA officials trying to defend parallel construction say they use it, "every day".