[turbojerry]

I have a trick too, ask about a worst case scenario, in the case of the NSA spying it might go as follows-

Given that throughout history every intelligence organization has been penetrated by those hostile to it, having a system like PRISM means that the hostile agencies would be able to do more damage to the USA that they would otherwise. A hypothetical case would be a hostile agency gaining information to blackmail a guard at a nuclear weapons storage facility, allowing the USA to be decimated from the inside with its own nuclear weapons stockpile.

Then allow them to contemplate it, be completely silent. There are really only two responses to this, either it starts to dawn on them that what they are doing could harm many innocent people or they will BS, not want to talk about "hypotheticals" and generally evade the possibility just laid out. The former means they are human, the second, probably a sociopath.