The point is not whether that can decrypt a selected target, rather it is that encryption causes a problem with surveillance from both a practical and legal standpoint.
First by encrypting your communications, you clearly establish an assumption of privacy, which isn't as obvious with clear text (IANAL, but I assume that creates a hurdle in the courtroom). Second, applications that take in massive data of warrentlessly available data streams don't have the facilities to hack each one and still provide timely indicators of malfeasance. This kinda relies on the first point, because if someone didn't encrypt their communications, one MIGHT argue that the communicatee didn't mean for it to be private.