Quis custodiet ipsos custodes? Or, roughly, in English, who watches the watchers? This question has been asked for centuries, to the point where it has become accepted as profound philosophy. But it's not.
To begin with, it leads to an obvious and immediate absurdity. Who watches the watchers? Well, then who watches the watchers of the watchers? And who, dare we ask, watches the watchers of the watchers of the watchers? Further...there's surely no need to take it further. You get the point.
So what is the actual point of the question? We won't bother about the original intent; that is easily enough found through a simple web search, and really has little bearing on how the question is asked today. It is asked today simply to dismiss authority. It is the question which the atheist asks of the God fearing and which the liberal or libertarian asks of the conservative whenever they wish to denigrate the proper authority of the state or the Almighty.
It is also not a question which needs to be taken seriously. In the first place, well, we've already addressed the first place. In the second place, it can be thrown right back in the face of the asker. They can be quite properly asked, who watches you? All that is accomplished then is a standoff; no one can morally go forward because, and perhaps this does tie into the original meaning after all (if you've done that quick search you'll know where this is going), everyone is fallible. Everyone is subject to doing the wrong thing, whether by intent or honest error, because we are not a one of us perfect.
Yet should we really employ that attitude, once we really actually accept that no action is legitimate merely because there is the possibility of error within us, then we can't take any actions at all. Anything we do may be corrupted; indeed, everything we would do is be bound to be corrupted. Indeed, every act by its nature, being caused by corrupt beings, would be illicit.
Obviously the world can't go on that way. All it can do is the best it can, through the best possible interaction of humanity at a given time. And then, when errors occur, we do our best to straighten them out. It's that simple.
Obnoxious questions which can only serve to show disdain for authority will not serve that calling. Yes, authority could be wrong. Yet it could be right. And that's the issue we ought to be concerned with when considering what we ought to do in our lives, both personally and politically.
Quis custodiet ipsos custodes? Ex uno disce omnes; from one we can judge the rest. Eh, maybe it isn't the best response. But it's a good enough one once we learn to recognize valid authority.