Hegelianism was an exercise in intellectual hubris which easily misled its followers into political hubris. Hegel's antithesis-thesis-synthesis structure came straight out of medieval law schools. This dialectical method was (and with some variations and changes of terminology still is) used where, under the facts of a dispute, the law as it stands is arguably ambiguous. Legal scholars analyze the legal arguments of plaintiff (thesis) and defense (antithesis) and reconcile these arguments in order to reach a just verdict and a more comprehensive and clear rule of law (synthesis).
Later in the Middle Ages, but still long before Hegel, the dialectical method spread, with variations and changes of terminology, to some other branches of university study (e.g. theology and science), but its success was still quite dependent on the availability of a rich set of facts from which to use the method to induce laws. Thus, for example, phrases like "law of nature" and "scientific law" stem from this origin of the inductive scientifc method.
The real value of dialectics in interpersonal matters comes from taking a specific dispute between two specific people, with very specific and well investigated facts, and inductively reaching a new clarification or minor variation on a rule of law, custom, or manners (synthesis) that achieves a just outcome for this dispute.
This is how the law is supposed to evolve, inductively, slowly, case by case over many centuries. This is how good law is "made" by judges. But in the hands of a dogmatic philospher like Hegel or Marx, dialectics became an exercise in faux implied omniscience -- the idiotic but compelling hubris we can trace the broad path of history itself through the movements of major opposing ideas (Hegel) or economic factions (Marx), and through this cabalistic exercise learn the "laws of history" which culminate in the idealistic outcome already desired by the philosopher, whether the supremacy of the State (Hegel) or an egalitarian utopia (Marx). Divorced from the reality of details and the patience of evolution, the outcome in real socieities, though labelled "progressive" (in honor of the direction of history as "discovered", i.e. as desired and cabalistically justified, by these philosphers) -- though called "progressive", the actual outcome was more often than not quite in the opposite direction. The actual outcome was analogous to what a genetic engineer would get if (with our limited knowledge of the workings of genes and the proteins they code for) said bioengineer cut and hacked thousands of genes and then reassembled them in a more "rational" manner. All that bioengineer would get out of such a naive and radical procedure is monsters and death. Our genetic code is far too complex to change more than a few genes at a time. Our interpersopnal relationships, and thus our society and our politics, is far more complex still. That is why we got even more monsters and death from Hegel, Marx, and their many naive and radical followers.