It never was a social program. It was really about socialism, but socialism's opponents kept that from happening.
The idea behind social security was to extract retirement funds from the private investment markets and put them in the hands of the government, which would "invest" them on behalf of retirees. The result would have been the World's Largest Mutual Fund, with enough money to buy controlling interest in the Fortune 500 and then some. Presto... government ownership of the means of production.
Enough people saw that coming, and opposed it, that the requirement that Social Security funds only be invested in government securities was inserted. The socialists were disappointed, but they could live with that because it still resulted in huge sums available for government spending programs, which are the next best thing (if you're a socialist) to owning the private economy.
One can only imagine what the size of the US economy might be today if all that money had been available for capital investment over all those decades... instead of being spent by politicians on near-term consumption programs to buy votes.