What do you mean? It sounds like it's completely public not private. How would it be abused?

It's invested in private firms (SS is in government securities), and it's abusable insofar as it is possible for those making investment decisions to pursue personal or corrupt agendas rather than the public interest. Except for scale, it's not at all unique in this way, every fund where managers act as agents with other people's money has this as potential abuse vector, and while many operate tolerably well most of the time, abuses are a recurring thing.