The NSA data is collected under search issued by a FISA court. So, during a suppression hearing, defense counsel can challenge the validity of the warrant. If their challenge is denied, they can appeal. If their appeal fails, they can petition the Supreme Court. In all these courts, the proceedings are public record and the standard for a warrant can be debated by lawyers and the public alike. We have an open process for checking the work of the humans issuing FISA court warrants; Use it.
Even if the warrant was valid, the NSA might have overstepped its bounds. This can also be challenged when the NSA defends the admissibility of its criminal evidence in a suppression hearing. An independent judiciary can decide if the executive branch has acted outside its bounds. No, an investigator isn't punished for the overbroad evidence collection, but they are embarrassed by having a criminal get off due to their sloppiness. We have an open process for checking the work of human investigators in this country; Use it.
It isn't as if the government just takes that evidence and unilaterally decides to blow people up. We have due process in this country; Use it.
/s