This argument by Carrol is one I can deal with more than most, but it assumes two things; (1) individual dedicated organizers have marginal effects, rather than playing key roles in sparking pyramiding circles of effect; and (2) that Marxists are no better at organizing than typical folks that the Dean campaign can hire.
In many cases, (2) may be true, so for all the incompetent Marxists out there, feel free to sit the election out. But I've known many Marxists who were also kick-ass organizers who could have very positive effects on an electoral campaign, both in making it more successful but also in changing its character. So having them involved will make a difference.
-- Nathan Newman