That depends on what they are doing and how they are doing it. If their only goal is to somehow bring about communism by winning a vote in a capitalist democracy, they are obviously ridiculous. But while living under a bourgeois democracy, while the population at large still believes in that system, participation in it can be used as a tool to build class consciousness, to work toward the ultimate goal of revolution. This is essentially Lenin's position in “Left-Wing” Communism: an Infantile Disorder.

Participation in parliamentary elections and in the struggle on the parliamentary rostrum is obligatory on the party of the revolutionary proletariat specifically for the purpose of educating the backward strata of its own class, and for the purpose of awakening and enlightening the undeveloped, downtrodden and ignorant rural masses. Whilst you lack the strength to do away with bourgeois parliaments and every other type of reactionary institution, you must work within them because it is there that you will still find workers who are duped by the priests and stultified by the conditions of rural life; otherwise you risk turning into nothing but windbags.