Actually, spying on citizenry is really the effect of democratic rule if you think about it.
Any body with political power will naturally try to preserve its power, just like anything likes to hold onto what it has. Thus it will do everything possible to insure that it continues in power. Anything that is a danger to the exercise of its power must be observed, controlled or eliminated or else one loses political power.
In a monarchy, the threats to power are usually other possible candidates to the throne, or, more commonly, foreign powers. Thus a monarch will do everything possible to eliminate possible usurpers or foreign agression. Examples of history are the War of Roses, or most of medieval Europe.
In a democracy however, the power devolves from the people, and so those in power need to know what the people are planning to do, especially on how they plan to vote, because this is the only real threat to their power. The power devolves more from public opinion, and so public opinion has to be known, observed and eventually controlled in order to stay in power. Since political power resides in the voting populace, there is a general tendency in any democracy to try to control the opinion of the populace, or at least to know the dangers to which their power is endangered. The phenomenon of gerry-mandering is nothing else than political power trying to insure its continuance.
In a monarchy the people are naturally subject to the monarch, and the enemies are usually foreigners. Thus in a monarchy there is not much need of a general program of spying on citizenry. In a democracy however the people elect their ruler, and so a democratic ruler, if he wants to continue to rule, generally treats the citizens themselves as a threat to his power. Thus he must spy on them, know that they are doing, just like any political power spies on its enemies.
Even Aristotle said that a democracy naturally degenerates into despotism. The United States is simply repeating the past, though one must say in a much faster tempo than its predecessors.