The Communist Party Is a Vanguard of the Proletariat

I don't remember the idea that the Communist Party is a vanguard of the proletariat. The ruling class has lost its function, but succeeds in clinging to power by force or fraud. So what was the bigger problem with communism? Sincere fanaticism or cynical opportunism? It's very simple. Of course, fanatists have more of a few because they were the one. But actually, I would say, the cynical opportunists was more important than a fanatical.