I believe fully that FDR knew exactly what he was creating.
I will concede one point though in FDR's favor, that being that he expected future politicians to improve the system instead of making it worse.
They not only have managed to improve the system, they have successfully turned back efforts by Reagan and Bush thatwould have decimated SS over time.
Socialism has been the goal, Social Security is simply one of the tools to achieve the goal.