You're asking a question with a loaded premise, no system is immune to problems like corruption. At the same time, the various systems of socialist democracy have been far better than capitalist democracy, and the reasoning common to all is that the working class is in control, rather than capitalists. Structure varies from state to state, but having a system where the input and direction of the working class is paramount is far superior to capitalist democracy.

In capitalism, it's democracy for the capitalists, dictatorship for the workers, in socialism it's democracy for the workers, dictatorship for the capitalists.

There's a lot of research and reading you can do on how socialist states function, and a lot we can learn from them.