It was … Hegel who established the view that the different philosophic systems that we find in history are to be comprehended in terms of development and that they are generally one-sided because they owe their origins to a reaction against what has gone before.—Walter Kaufmann, From Shakespeare to Existentialism (Princeton, NJ: Princeton University Press, 1980), pp. 95-96.
If Hegel meant this charge of one-sidedness as a criticism, then he was misguided. What Hegel observed in the history of ideas is exactly what Darwin observed in the natural world. It is the fundamental process by which evolution takes place, whether biological or otherwise. In the natural world, new biological forms develop as a reaction against something adverse in the environment (that is, something that threatens survival). Darwin called this "natural selection." But the general principle is not necessarily restricted to nature. In the history of ideas, a similar process is at work. Kaufmann's phrase "what has gone before" is somewhat inaccurate. Thinkers react not against what has gone before, but against what currently prevails. If a current system of thought proves inadequate to explain what we know about the world, or have just come to know about it, then it gets challenged and is sometimes discarded, sometimes amended and adjusted to address the areas in which it is wanting.
This is not one-sidedness (if by one-sidedness we mean lack of "proper" balance). It is precisely how development works. Evolution, whether of biological species or of ideas, is a hit-and-miss game, a trial-and-error process in which issues are addressed on an ad hoc basis. The principle of economy demands this—a principle recognized both at the "high" end of the spectrum in the form of Ockham's Razor and at the "low" end in the folksy adage: "If it ain't broke, don't fix it."
Following Hegel's lead, one could complain that the history of technology is "one-sided" since inventions are, for the most part, inspired by what is lacking or deficient in the current state of affairs, that is, as a dissatisfaction with and a reaction against what prevails at any given time. When mousetraps don't work as efficiently as we would like them to, someone comes along and invents a "better" mousetrap. If everyone is satisfied with the most recent type of mousetrap, no one would feel the need to spend his or her energy on inventing another kind, just for the sheer delight of having another kind of mousetrap. It is, after all, necessity that is the mother of invention. (It must be recognized, however, that in the area of technology these days, it is often the desire for monetary gain that inspires invention rather than necessity.) And like technology and biology and just about everything else, philosophy and the history of ideas is driven by necessity—not necessity in the Hegelian sense of logical necessity, but in the practical sense of needing something more adequate for the prevailing conditions.
Of course new philosophical systems are reactions against prevailing ones! What else would they be? And of course, the history of ideas is a history that proceeds "negatively" (that is, as a reaction against something, an attempt to negate it). This is no great surprise. Hegel thought that he had devised the philosophical system that would end the creation of new philosophical systems (and thus bring to an end the history of philosophy). How would this be accomplished? He thought he would avoid the "one-sidedness" trap by not reacting against what had gone before. His system would start from scratch and end with the Absolute. It would be the first and last word in philosophy, and it would be perfect. Ironically, there was a flood of reaction against Hegel in the years following his demise. He wasn't, after all, the last word in philosophy.
Hegel has come and gone, and philosophy still goes on, pretty much without him.