Marx was not a philosophical liberal, unlike, e.g., J.S. Mill. He was a distinguished critic of liberalism. That is different from whether he was a harsh polemicist. One may be an anti-liberal philosophically but a gentle-manly/-womanly/civil interlocutor, Marx was not.
Like Dinsdale in Monty Python's Piranha Brothers:
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CB: That's true. Also, anti-eclecticism and "authoritarianism" are different. Use of the word "authoritarian" to characterize a claim that Marx was not a liberal is a malappropism.
By using harsh polemics against liberals, Marx made it clear that he was not a liberal. He didn't use bourgeois finesse in criticizing the bourgeoisie. Form and substance were united in that.