I don't think the parent was trying to absolve the NSA of responsibility, merely pointing out that its mission incentivizes it to collect as much data as it can

I don't think the parent was trying to absolve the NSA of responsibility, merely pointing out that its mission incentivizes it to collect as much data as it can. It's ultimately the responsibility of Congress to ensure that the NSA and other intelligence agencies adhere to the law, and Congress has largely ignored this responsibility. The more subtle point that the parent makes is that, rather than always trying to prevent bad actors from doing bad things (e.g. murdering), a working system of checks and balances can punish the bad actors and deter future abuses. But checks and balances obviously don't work when everything is classified. The legislature and the judiciary were essentially the only two institutions that had access to this information and they did nothing about it. You can't vote judges out of office, but if large scale surveillance is an issue important to you I'd make sure my congressman or congresswoman knew about it.