How do you propose making it mandatory then?
Otherwise, we'll have to argue whether elderly people who didn't invest should be allowed to starve in alleys.
And there you have it. The progressive argument in a nutshell and the ruling class relies on this to maintain their power over the individual.
If someone fails to properly plan to be able to retire, then they would have several options. We don't need a heavy handed, ironfisted, centralized system in DC. They could:
1. Continue working
2. Be supported by family members
3. Get charitable help from their local Church / Synogogue / Mosque
4. Work with other local charitable organizations
5. Localities (cities, towns, counties) could set up charitable organizations
6. States could fund the safety nets