The answer to "What's wrong with communism?" is very different from the answer to "What's wrong with Marxist-Leninism?" To the former, we might answer, "Nothing, if you can make it work. The first century Christians had a common purse. It's just tough to sustain, especially on a large scale." To the latter, let's consider Blessed Father Jerzy Popieluszko.
Ordained in Warsaw, Poland in 1972, he worked closely with the Solidarity movement until his arrest on trumped up charges. When the Church announced its intention to fight the bogus charges, they were dropped. He resumed very vocal criticism of the government and support for the workers of Poland.
On October 19, 1984, the Sluzba Bezpieczenstwa (Security Service of the Ministry of Internal Affairs) kidnapped Father Jerzy, beat him to death, and then dumped his body in the Vistula Water Reservoir where it was found ten days later. Although several of the secret police were busted for the crime, their sentences were light.
Marxists, in pursuit of their pure Communist state, abandoned their dedication not only to freedom, but to the very workers they sought to liberate. As the menace of the USSR and its satellites fade, it is good to reflect on the persecution of the faithful that those regimes ordered.