I think they are more cause than effect, unspun. For they shape the very "climate of opinion" in which everything else happens. If I had said "Karl Marx," instead of Hegel or Derrida, my point probably would have been instantly grasped.
Marx got most of his "bright ideas" (i.e., his "dialectical method") from Hegel. He is too early on the historical timeline to be a full-blown "deconstructed self"; but he has been an incredibly influential thinker of the modernist, so-called "disinterested spectator" type, and (arguably) a true gnostic. He literally transformed the world.
He sees the world as something completely "objective" to himself -- that is, as already "complete" in time and "apart" from himself, as something he has the power to "master," to transform into shapes more pleasing to himself -- he's "free to rearrange the furniture" anyway he wants to, to his heart's content, in the interest of "perfecting" the institutions of human existence and, along with them, the human condition. (I assume he had a heart -- it's just not terribly obvious, given what his "students" -- among them Hitler and every communist living or dead) have done to society over the past 150 years or so.)
The fatal fallacy he commits, however, is to think of the world as something subject to his direction in the first place, as amenable to his will. Yet he is only a part of the world, not a directing genius that somehow stands outside of the world. That is to stand in the role of God (which is why Marx had to bump Him off to begin with). The part does not and cannot constitute the whole of which it is a part. The world is not our private "toy" to play with. To think that the part can do this is a total fantasy.
Yet a compelling fantasy, as it appears: Marx's "followers" are legion. His "thought" has been thoroughly internalized by many people, some of whom are incapable of even analyzing or critiquing it. It's just become part of the Zeitgeist -- or the "Kultursmog" -- the "climate of opinion." And it relentlessly continues to undermine human liberty and civil society, everywhere it gains a foothold.
I don't dispute the power of thinkers and theorists to manufacture ideas, but those who distribute them into marketplace and those who consume their communicable agents and use them for excuses for their graspings for power, money, fame and sex (or virtue) seem at least as significant to me.
I think Hitler, Lenin, Mao, Hefner, Friedan, and company (or the Adams brothers, Patrick Henry, the numerious post Great Awakening pastors, etc.) would have still grasped whatever rationale they could muster, to do make their assessments and plan their actions.
Also, it is most often the case to find not one singular theorist moving the world so to speak, but getting into the culture's Patent Office just a few days ahead of the next one, and all taking up where others leave off. Marx had many who went before to choose from and so did his mentors, and so did those who came after him. Often we find that there is one especially determined/creative figure in the "right time and the right place" who lays hold of more material and makes more advanced designs out of it all (hm, laying aside the matter of "thinker vs. doer": ...Plato, Machiavelli, Luther, Th. Aquinas, Marx, Edison, Frued, Beethoven, Einstein, McCartney?, Bill Gates, to name a few) but these are a part of the developmental flow too, with progenitors, peers, and offspring.
All economies seem demand driven, including those of thought and belief, eh?