As much as Bernie would like to blame the money laundering and money-hiding in the Panama papers on capitalism, in fact the vast majority of clients in those papers appear to be from socialist and strongly interventionist, populist governments.
Socialist countries tend still have winners and losers just like capitalist countries. However, those winners and losers are not determined by success in making products and services in the marketplace, but in success in reaching a leadership position in the government or cozying up to those in government. Soviet government elite had special privileges and special stores not accessible by ordinary Russians. The Castro brothers and Hugo Chavez's daughter are among the richest people in the western hemisphere.
However, these wealthy leaders now have two problems. First, they likely spend most of their time spouting egalitarian claptrap, so that they would like to hide their wealth in order to mask the obvious consistency problem. Perhaps more importantly, their socialist policies have likely destroyed the country's economy -- there is, for example, no place any sane person would want to invest a billion dollars in Venezuela. They need to get their money out of the country but because everyone else in a socialist country is also trying to get their money out, the self-same leader has likely instituted capital controls. So the leader needs to put his or her money in a different country where it can actually be invested productively, and in doing so must evade their own capital controls.