Simple test - which kinds of incentives one uses for purpose of having anything done:

- market incentives (do it and you'd be rewarded)
- force (either you do it or you'd be deep in trouble)

*[Sure, there could be some social /religious  / ideological pressure, but at the end of the day you just do it because you'd gain / not lose your social capital]* 

As one see there is a big problem from communists perspective. Sure, one may reward top workers and Party members with ex. access to deficit goods. However, if that is being used on bigger scale, then you start getting for practical purposes high level of social inequality. (Sure, everyone can buy a car, just a Party member would skip 10 year queue and actually get it, instead of having it just vaguely promised like the rest of society). Some level of inequality and semi-market approach could be applied without being accused of failing orthodoxy, but still force is necessary.

How can one keep highly skilled and high working labour force, when if they had a freedom they would escape to capitalist countries and earn there more? East Germans at first thought that they can allow an open border, as they would get a safety valve (like loosing potential trouble makers) and not a severe brain drain.

Similarly, even kept inside, people may come up with their own business ideas. Either one squash them (or at least cap their growth potential through draconian regulation) or soon would face nimble entrepreneurs outcompeting government institutions.

So yes, in order to have communists society you need to force people to do multiple things that they don't like, including forcing them to stay. Authoritarianism is not a degeneration, but logical choice when you have to force people to behave according to ideology expectations and have limited ability to buy them off.