For instance, there was considerable unhappiness with the Party's decision to outlaw other parties and later, to ban factions inside the Party. Some people reasoned that if one Party is good, more parties must be better. The reason the Bolsheviks outlawed the other parties was that all the other parties were being used as tools by the capitalists in their drive to reconquer power. The battle between workers and capitalists will heat up after the revolution, and the capitalists will use every opportunity to organize. The working class needs to be united against the class enemy.
Some people think that having one party stifles discussion and disagreement.
Some people worry that the Party may go revisionist. But having many parties is only an excuse for revisionists to organize under the cover of another party. If the one party were to be taken over by revisionists, then communists would split the party, found a new party dedicated to the violent overthrow and suppression of the revisionist party. These soviets were usually organized on bourgeois democratic lines, and they had the usual faults of bourgeois democratic institutions. Syndicalism is basically capitalism based on workers' cooperatives.