Anarchism: Ruining any Meaningful Advance of the Left Since 1867.

That's not even some lack luster liberal opinion. Communists and socialists that have actually accomplished something have long done their best to keep this kind of ineffective garbage from happening as it just ruins any sort of actual organization.

"This latest Fenian exploit [an act of terrorism] in Clerkenwell is a great folly. The London masses, who have shown much sympathy for Ireland, will be enraged by it and driven into the arms of the government party. One cannot expect the London proletarians to let themselves be blown up for the benefit of Fenian emissaries. Secret, melodramatic conspiracies of this kind are, in general, more or less doomed to failure."
-Marx, 1867 letter to Engels

"Here, then, is the immense difference between the Socialist Republicans and our friends the physical force men. The latter, by stifling all discussions of principles, earn the passive and fleeting commendation of the unthinking multitude; the former, by insisting upon a thorough understanding of their basic principles, do not so readily attract the multitude, but do attract and hold the more thoughtful amongst them. It is the difference betwixt a mob in revolt and an army in preparation. The mob who cheer a speaker referring to the hopes of a physical force movement would, in the very hour of apparent success, be utterly disorganised and divided...The army of class-conscious workers organising under the banner of the Socialist Republican Party, strong in their knowledge of economic truth and firmly grounded in their revolutionary principles, would remain entirely unaffected by any such manoeuvre and, knowing it would not change their position as a subject class, would still press forward, resolute and undivided, with their faces set towards their only hope of emancipation – the complete control by the working-class democracy of all the powers of National Government."
-James Connolly, 1899

"But the disarray introduced into the ranks of the working masses themselves by a terrorist attempt is much deeper. If it is enough to arm oneself with a pistol in order to achieve one’s goal, why the efforts of the class struggle? If a thimbleful of gunpowder and a little chunk of lead is enough to shoot the enemy through the neck, what need is there for a class organisation? If it makes sense to terrify highly placed personages with the roar of explosions, where is the need for the party? Why meetings, mass agitation and elections if one can so easily take aim at the ministerial bench from the gallery of parliament?

In our eyes, individual terror is inadmissible precisely because it belittles the role of the masses in their own consciousness, reconciles them to their powerlessness, and turns their eyes and hopes towards a great avenger and liberator who some day will come and accomplish his mission. The anarchist prophets of the ‘propaganda of the deed’ can argue all they want about the elevating and stimulating influence of terrorist acts on the masses. Theoretical considerations and political experience prove otherwise. The more ‘effective’ the terrorist acts, the greater their impact, the more they reduce the interest of the masses in self-organisation and self-education. But the smoke from the confusion clears away, the panic disappears, the successor of the murdered minister makes his appearance, life again settles into the old rut, the wheel of capitalist exploitation turns as before; only the police repression grows more savage and brazen. And as a result, in place of the kindled hopes and artificially aroused excitement comes disillusionment and apathy."
-Trotsky, 1911

"First, that party, which rejected Marxism, stubbornly refused (or, it might be more correct to say: was unable) to understand the need for a strictly objective appraisal of the class forces and their alignment, before taking any political action. Second, this party considered itself particularly "revolutionary", or "Left", because of its recognition of individual terrorism, assassination—something that we Marxists emphatically rejected."
-Lenin, 1920