[mikekchar]

On the other hand, consider a computer system. If you wish to have a secure computer system, you try to design it in such a way so as to make undesired behaviour impossible. For example, we spend a lot of effort looking at weaknesses in our systems and saying, "Well, someone could overflow this buffer here and get root access". Our reasoning is that if it is possible, it is probably only a matter of time before someone actually exploits it.

So while I completely relate to your feeling of trying to avoid conspiracy theory fantasies of "how do we know they haven't done that", I think it is probably not a good idea to say, "[this] is one of those things that we can safely not consider, even though it is... technically and politically possible".

Whether or not it has happened in the past, we probably don't want it to be possible and we probably should consider to consequences of what would happen if the government decided to take that action. 'Eternal vigilance is the price of liberty,' and all that rot.