I'm sorry but calling the USSR a "vanguardist dictatorship" is just not historically accurate. Plenty of democratic mechanisms in the USSR, at any rate much better than anything else we've had so far. For a dictatorship, it dissolved itself quite peacefully didn't it?
Sadly, attempts at socialism in which workers didn't take the power of the state, ended up like Salvador Allende in Chile, like Mosaddegh in Iran, like the Spanish Second Republic... Idealism only gets you so far, sadly.