I disagree that this argument involves a fallacy. The following statements are not equivalent:
1. It seems like at that point it should deny every single request going forward until the illegal activities have stopped.
2. Every request going forward is illegitimate.
(2) is false, but I believe that (1) is plausible, especially if there are any difficulties for FISA to determine whether any particular NSA request is legitimate or not.
Not necessarily. The court can do (1) in order to punish the government for not complying, similar to excluding improperly obtained evidence that would otherwise be relevant.
Only if you define "legitimate" so that what you say is tautological; not if "legitimate" means, for example, "concerning a targeted and specific terrorist threat".
1. It seems like at that point it should deny every single request going forward until the illegal activities have stopped.
2. Every request going forward is illegitimate.
(2) is false, but I believe that (1) is plausible, especially if there are any difficulties for FISA to determine whether any particular NSA request is legitimate or not.