Joseph Schwartz writes that "Revolutionaries such as Rosa Luxemburg and Victor Serge criticized early Soviet rule for banning opposition parties, eliminating experiments in workplace democracy, and failing to embrace political pluralism and civil liberties. If the state owns the means of production, the question remains: how democratic is the state?"
They both did this, no? Serge's criticisms were later than Rosa's of course. But they both made such criticism even as they defended the Bolshevik revolution itself and remained opponents of right-wing social democrats and the anti-Bolshevik Kautskyist "center."