Contrasting the anarchistic or libertarian socialists at the tip of the range with the Leninists and social democrats, Frank Girard (an anarchistic socialist) comments:
But if they are splintered, our ‘force’ is atomized consisting of small groups and grouplets each with its own publication and small circle of members and sympathizers. Except for the Socialist Labor Party (SLP) and the Industrial Workers of the World (IWW) – historically mortal enemies although they share an identical view of socialism, the groups are local, isolated” and like the IWW and SLP, often mutually hostile or at least suspicious. 
There is nothing in socialist, anarchist, Marxist or communist theory to explain why two groups holding “identical” views of socialism should be mortal enemies, or why the whole movement, from social democrats through Leninists to anarchists, should be divided into sections which are splintered and, towards the extreme, atomized, isolated, often mutually hostile or at least suspicious. Beyond Politics shows how this condition arises in the course of ideological development.  Discussion Bulletin No. 49.
from Ideological Commentary 54, Winter 1991.