Are the concepts of freedom and working towards collective good so mutually exclusive?
Not necessarily, and I also disagree with the commenter above that without the USA suddenly the world would be singing kumbaya.
The problem was dictators seizing power in turbulent times. In Russia, Stalin abolished the soviets (A.K.A worker's councils, kinda like mega unions) in the Soviet union. I think that says a lot.
In Romania (I'm a bit better equipped to talk about this one), things were a bit different.
The original communist government (1945) was essentially a Russian puppet state that drained the wealth of Romania via war reparations. Stalinist purges happened often during this period.
During the 1950s and early 1960s, Romania got a degree of independence and things were actually looking up. Society in general (infant mortality, gender equality, literacy, standard of living, etc) were all improving rapidly without Russia draining us and making decisions for us, and we didn't have a surveilance state of the scale that would come later. This was a period marked by political battles between the liberal communists and the Stalinist communists for control, with Stalinists commiting some pretty horrible atrocities (if you want nightmare fuel for some reason, look up the Pitesti experiment).
Then, 1965, Ceacescu took power. During his early years, he actually looked like a liberal (EDIT: Just to be clear: I mean a liberal communist. This means more individual freedom for citizens in a communist economy). He allowed some emigration, some free speech, and even spoke out about the 1968 invasion of Czechoslovakia. This, at the start, did not look like a typical authoritarian communist state. Unfortunately, Inspired by the "amazing" society of North Korea in 1971, he started to make changes in the structure of society to be more like it, which included an expanded Securitate. 2 years later, harsh austerity policies to repay foreign loans led to a massive drop in living conditions, which led to riots, which led to crackdowns. Things rapidly spiralled, and the Securitate were given more and more power to keep control.
This then became the police state that everybody thinks of when they think of communism. A combination of too much power in 1 person's hands, an authoritarian imperialist overlord (Russia), and rising backlash against dropping living conditions.