Democratic ideology essentially contains two sort of the illusions:
These illusions have many forms and are interrelated. Mainstream American democratic rhetoric justifies political decisions by the use of both elections and polls. It is "very democratic" in the sense that the passive choices of the majority can change the form that the American repression and exploitation take.
Worker's self-management is a more obscure form of this illusion which claims that the changes in the way a factories' decisions are made will change the form that an entire society will take. It's basic position is summarized in the sticker that calls for workers to "fire" their bosses, and apparently continue production in the same old way.
It is important for revolutionaries to oppose both versions of democratic ideology. On one hand, after a revolution there certainly won't be any reason to fixate on the process of reaching each decision. For example, one person could be assigned to decide a day's delivery schedule in a communal warehouse without oppressing the other workers - who might prefer to spend their time walking on the beach. This dispatcher would have no coercive power over the other participants in the warehouse and deciding the schedule would not give her power that she could accumulate and exchanged for other things. For their own enjoyment, the worker might on the other hand want to collectively decide the menu of a communal kitchen even it was a less efficient use of time.
On the other hand, it's important to realize the no scheme for managing society will by itself create a new society. Highly democratic, highly authoritarian and mixed schemes are now used to administer capitalism. The basic quality of this capitalism that the average person has little or no control of their daily mode of living. Wage labor dominates society. You must exchange your life to buy back your survival. Whether the average person under capitalism might somehow be able to make a large of decisions about which records they buy, which inmates serve long sentences, what the color the street lights are, etc. is irrelevant.
The community that escapes capitalism will involve people effectively controlling their process of living. This the individual and collective refusal of work, commodity production, exploitation etc. This certainly will require a large amount of collective decision making and a large amount of individual decision making. The transformation cannot be reduced to a set way of making decisions or a fixed plan of action.
The different modes of living are easier to describe using Marxian terminology sometimes because it speaks in terms of social processes rather than atomized individual actions. The economy is both a way people make decisions and a way people act. You can only see the real conditions of society by looking at the conditions of daily life - how a society's mode of existence reproduces itself. This is summarized fairly well using the Marxian terms of political economy, spectacle, commodity etc.
All forms of democratic ideology appeal to a model of human behavior that implies each person is wholly separate social agent that only affects others in fixed, definable ways. This is the language of "common sense" in a world where people's senses are controlled by capitalism. It defend the right, for example, for a man to shout cat-calls at woman who has previously been raped because that man's actions are simply "free speech" not connected to any social action.
Communist positions see a social web which to not reducible to a fixed number to definable relations. Communists do not say that without capitalism we can guarantee that humans will create a human community. It says with capitalism, humans cannot create a human community. It sees that any movement for a human community will oppose capitalist social order and social relationships all along the way. The motivating force will not come with a communist blue-print but from the process of living of proletarians creating a new social relation.