Sam, I think you are confusing causality with what Max Weber called "elective affinity." Theory or philosophy by itself cannot cause anything but insomnia, let alone change society. Social change is brought about by people who control material resources that are vital to society.
However, as Marx wrote: "Men [sic!] make their own history, but they do not make it just as they please; they do not make it under circumstances chosen by themselves, but under circumstances directly encountered, given and transmitted from the past. The tradition of all the dead generations weighs like a nightmare on the brain of the living." Stated differently, the intersts of the ruling class who control vital material resources must be dressed in the aura of legitimacy if they are to be accepted by society.
Hence the need for the proper theory or philsophy with the appropriate elective affinity to the elite interests.
Another way of looking at it: philosophy and theory is like a garbage can - full of various crap. Different pieces of that crap are picked by different people for different reasons and to different ends. The crap being picked by the ruling class which "has the means of material production at its disposal" to legitimate its social class position becomes the dominant ideology, philosophy or theory of the time.
wojtek