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.