The disadvantage is the same as with 401ks and the like: such a system would require every citizen to have a relationship with a fund manager. At least 401k is

The disadvantage is the same as with 401ks and the like: such a system would require every citizen to have a relationship with a fund manager. At least 401k is opt in and voluntary. Wall street would love such an arrangement, and they get guaranteed capital locked up in their shenanigans, and guaranteed management and brokerage fees from every adult citizen. And, the actual capital for these investments is still what it is, so they'll find a way to make sure that people holding these default free shares don't benefit from them significantly.