I believe a proper understanding of Marxism and a general disspelling of generalizations should be taken in defense of Marxism, and I think foremost and most important of all is class struggle, without Marx's concept of historical materialism socialism maybe just be a fascist movement. Marx posited that historical material conditions formed the basis for class struggle, and that the proletarianization of the working class bring a sharp divide in the material interests between the proletariat and bourgeois. You must understand therefore the two economic dictatorships: the dictatorship of the bourgeois and the proletariat - both are the absolute opposite of each other, and both breed opposite results in material conditions.

Think of it like this, the bourgeois dictatorship as the opposite of the proletarian one will naturally make horrible material conditions, and naturally cause more division and class struggle between the rich and poor. The proletarian dictatorship (socialism) is the opposite and breeds better material conditions because the interests of the proletariat are the same of those of humanity, and thus that's why economic socialism breeds communism, class barriers are broken down through the struggle of the workers to destroy the bourgeois.

Socialism in definition is an imperfect implementation of collectivist ideals, and thus contradictions and reactionary tendencies will remain in this society, so the bourgeois (and classes themselves) will continue to exist in socialism, although class struggle is the active praxis(process) by which these contradictions are righted and more communistic relations of production are formed.

Socialism posits that proletarianization, that is proletarian control over the means of production (ie economics) breeds a more communal society and thus destroys bourgeois tendencies and attitudes. Thus socialism is equality in economics, communism equality in everything, life itself.

As to your question of Terror, the stage of 'terror' against the bourgeois in my opinion is a short-term one, I would call it the phase of 'direct reaction' by which the desperate bourgeois are still an active and conscious (important to remember this) class, and thus still act in their own interests, which are to resist the proletariat. This is a 'war' in the direct sense of the word because it's straight after the revolution, as Lenin's terror was straight after the Russian revolution. This is because it's straight after the bourgeois dictatorship is overthrown and the proletarian one replaces it, this is an unstable time and the ousted bourgeois class will actively resist through armed struggle, subversion and sabotage, the Whites and Tsarists in the Civil War are a good example of this.

Now after this 'direct phase' of class struggle under socialism, the bourgeois are dispersed and are no longer the coherent class entity, I would call this phase the 'revisionist' period, no country has yet passed this. In this stage the bourgeois are embodied in a passive, conformist, yet nonetheless dangerous, party element. Under the guise of 'reformism', 'democracy', 'openness' or whatever doctrine they claim to purport, the content is always the same.

Anti-revisionism, as a school of Marxist thought, seeks to combat the revisionist tendencies within varying schools of Marxism that deviate from the Marxist-Leninist line and employ a varying assortment of means towards conciliatory ends. Whether this be realpolitik, economic pragmatism, policies of "openness," and reform to outright denunciation and discredit of the past. It's a vile tumour amongst Marxists that has been used by opportunists to propel themselves to positions of mainstream acceptance and power (depending on the situation for which said revisionist may find himself in). The point being, anti-revisionism is a broad concept designed to combat the revisionist tendencies in Marxist thought and the political activities of revisionist organizations that inherently (by design or accident) betray the working class.

Thus this stage of class struggle displays the elements of 'quasi-direct' reaction to socialism, and although it maybe indirectly supported by bourgeois interests abroad - usually in the form of pragmatic nations, in the actual party itself the tendency is usually an unconscious reactionary tendency, disguised in terms of 'freedom' or 'democracy'. It's most recognizable trait is a desire to 'conform' to the standards of bourgeois statehood, to be recognized on the stage of bourgeois states and to participate in their games of 'international relations'(jingoistic bourgeois self-interest), or simply the 'big boys club'. But as always a dedicated and professional vanguard party usually utilizing a measure of self-criticism can combat this.

And finally it would seem the final stage of class struggle to be eliminating the last unconscious reactionary contradictions in society, these contradictions are of course not a conscious active group, but just tendencies which remain, but can be overcome by self-criticism and active aggravation of them until the relations of production are truly communistic.