Since internecine means "Of or relating to struggle within a nation, organization, or group; Mutually destructive; ruinous or fatal to both sides; Characterized by bloodshed or carnage", and The "Libertarian Communists" are essentially Communists with an ideology antithetical to ours, any "warfare" between us would hardly be "internecine".
But of course, you knew that, just as you probably know that a dictionary definition is unlikely to give justice to an entire philosophical ideology.