I gave you a plethora of actual evidence of human rights in an actually existing socialist country
Yeah, Cuba. Where everyone is poor w/o any major scientific and cultural influence in the world.
And yeah, USSR. They did try to influence the world but its internal economy was so shit that it couldn't even exist for 100 years and was a one party authoritarian regime. In the end it started to shift towards to capitalism. Also they supported the Nazis during Poland's invasion. The population who was so frustrated with their country that they toppled the Berlin Wall when USSR was collapsing.
But please elaborate: why is the nationalization and collectivization of means of production so vulnerable to greed?
Because the very nature of life I explained to you earlier. Life evolved in such a way that it is the survival of fittest, which requires hogging up all the resources as much as you can. Greed is ingrained in every living being's DNA.
Even you are greedy to want to divide all the wealth equally because for you it might be the only way to get richer than you currently are. It is not a matter of if being greedy is right or wrong, it is a matter of if your greed is so high that it destroys other people's lives and where to draw that line as a civilized society.
All the “center-left checks and balances” with strong union membership in the 1960s-1980s disappeared overnight
They never existed in practice in the U.S after the collapse of the USSR because communism failed and thus the perception swayed towards the extreme capitalist way. Later the extreme lobbying by the wealthy and anti-left got rid of the whatever regulations of systems that didn't allow them to be absurdly rich. It is called lobbying in the west while we call it corruption.
Before that when the governments didn't used to only work for the wealthy, the system was performing better than any other one. Europe's War Torn economy was improving, The US was in its golden economic age and all this while people overall had more rights and freedom than any socialist and communist regime. It started to go haywire when the extreme capitalists started to take over and the government stopped working for all the people but only for the rich.
There is no point in living in an extreme capitalist and a fascist country nor there is a point living in a poor socialist or communist country.