Moreover, the natural development of economic antagonisms, the waking consciousness of an important fraction of the proletariat, the constantly increasing number of unemployed, the blind resistance of the ruling classes, in short contemporary evolution as a whole, is conducting us inevitably towards the outbreak of a great revolution, which will overthrow everything by its violence, and the fore-running signs of which are already visible. This revolution will happen, with us or without us; and the existence of a revolutionary party, conscious of the end to be attained, will serve to give a useful direction to the violence, and to moderate its excesses by the influence of a lofty ideal.

--Ericco Malatesta, Anarchy and Violence

The beginning of that quote is worth adding for context for folks unfamiliar with Engel's argument here:

Why do the anti-authoritarians not confine themselves to crying out against political authority, the state? All Socialists are agreed that the political state, and with it political authority, will disappear as a result of the coming social revolution, that is, that public functions will lose their political character and will be transformed into the simple administrative functions of watching over the true interests of society. But the anti-authoritarians demand that the political state be abolished at one stroke, even before the social conditions that gave birth to it have been destroyed. They demand that the first act of the social revolution shall be the abolition of authority. Have these gentlemen ever seen a revolution?

And his conclusion:

Therefore, either one of two things: either the anti-authoritarians don't know what they're talking about, in which case they are creating nothing but confusion; or they do know, and in that case they are betraying the movement of the proletariat. In either case they serve the reaction.

The short entire essay is worth reading for other folks reading.