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.
We communists want to see a collective solution, with workers as a class running society as a whole, not competing with each other. The Chinese revolution also had a mixed experience with respect to communist democracy. The Chinese Communist Party made a lot of rotten concessions to the capitalists, including letting them keep some small bourgeois parties. The good thing that the Chinese Communist Party did was to develop the concept of a mass line. The Chinese Revolution advanced to the left whenever this concept was put into practice, as during the Yenan period, the Great Leap Forward, and the early part of the Cultural Revolution.