Manipulation increased rapidly in the last few decades. Why is this? The twentieth century brought enormous social changes to Western society. Primarily these changes involved the concept of universal suffrage, a movement towards a more humanistic society, an increasing emphasis on democratic institutions and a popular demand for accountability.
Political violence still happens, but it occurs less and less within our own societies. Government has tended to become more "scientific", more targeted and more systematic. Their methods of government parallel the development of "scientific management techniques" initiated by Ford, Taylor and the other early 20th century industrial modernisers.
Political manipulation as a sophisticated means of government fits in nicely with the tendency to use more systematised methods in management. Corporate interests have mirrored the increased interest in manipulation as a means of achieving strategic objectives, although it's not entirely sure whether corporate interests lead governments or vice versa.
Either way, manipulation is now fully fledged as a politically "legitimate" method of government which most of our modern politicians, civil servants and managers don't even think twice about.
If we remove the moral overtones, we begin to understand why manipulation is so very "useful" as a means of social control.
Manipulation can be perceived as "useful" for several reasons depending on whether you look at it as a sociologist or from the point of view of the manipulator:
Low Cost: Manipulation is an efficient method of social control because it achieves its results with relatively low costs.
Low Violence: Manipulation avoids more coercive methods and reduces political violence. It can achieve the same results with much less bloodshed.
High Deniability: Many acts of manipulation are highly deniable. A carefully designed manipulation can be totally secret and can be almost completely covered up and made untraceable.
No Consequence: Manipulation does not usually cause the often unpleasant consequences of coercion such as revenge against the manipulator.
Democratic: Manipulation is a relatively democratic technique, by which we mean that many manipulative techniques are available to many or all of us. Many of us are already using these techniques in some way every day.
Manipulation tends to "level the playing field" between those that have a lot of power and those that do not. Most of us have experienced manipulation in one form or another - maybe by that pushy sash windows sales guy? In this sense manipulation supersedes coercion as a means of social control, and balances the disparity between powerful and powerless