Marx and Engels seem to be particularly exacerbated by the way that Hegel's own way of doing things is reflected in their work.
Hegel is notorious for his defense of autocracy.
He makes a case that a robust constitution is the best defense for freedom, but then argues that the only way to get that strength is through a living figure, hence an autocrat.
The dialectic method is a great defense because "you don't understand the argument" but it also is built on obscurantism and the embrace of contradicting things, including the evidence for the Hegelians' own points.
That is easily the most succinct description of Hegelian philosophy I've ever read. Furthermore, it explains perfectly something rather noisome I've noticed about German philosophy and culture in general, as contrasted with English philosophy (the origin of liberalism, of course). German culture is extremely rigid in its structure and prone to authoritarian thinking; I have noticed that, if one wishes to get a German to behave a certain way, one need only tell them "it's the law," and most won't question it (which, believe it or not, contrasts quite clearly with certain other cultures I could name).
I may, perhaps, be putting the cart before the horse myself, as I don't really know if this aspect of German culture inspired Hegel or was derived from his work, but the connection is nonetheless apparent.
Some Hegelians are people who have little in the way of an association with authoritarianism (e.g. Stirner), but it's fair to say that Continental philosophy more broadly has strains of absolutism and autocracy that you don't see in the liberal strains of England and the like. Some Austrians are noteworthy exceptions (Mises and Kuehnelt-Leddinh are good examples of Austrian liberalism) and there are liberal strains in some continental schools of thought.
I'd argue that Hegel is more of a paid courtier coming up with justifications for the political order, which is Popper's theory. Of course, he's also incredibly self-contradictory and Hegel fans will complain that people don't understand Hegel. The crisis of the 1800s as far as politics in Europe goes was something like what to do with the decline of monarchies, so there's a lot of weird stuff going down.
If Popper's theory is correct, that's funny and sad at the same time. Then again, maybe it's funny only because I enjoy dark humour. As far as the difference between English and Continental philosophy, the correlation seems to apply only to the western part of the continent. Northern and Eastern Europe are rather different, probably because of far more loosely-structured societies (to be expected with a lower population density).
Returning to the "it's the law" line used to manipulate people, I've noticed certain centuries-old stereotypes that I find rather humourous, and also somewhat enlightening (i.e. a tiny reflection of the culture). Perhaps you might as well.
A Chinaman will respond enthusiastically and comply.
A German will say nothing and comply.
A Russian will say nothing, then do whatever he wants as soon as your back is turned.
An American will give you his opinion on the law, then do whatever he wants right in front of you.