Few people would classify legalized theft as an investment. An investment is generally considered to be voluntary.
in·vest·ment [ in véstmənt ]
use of money for future profit: the outlay of money, e.g. by depositing it in a bank or by buying stock in a company, with the object of making a profit.
money invested: an amount of money invested in something for the purpose of making a profit.
something in which money is invested: something, e.g. a company, endeavor, or property, that money is invested in with the goal of making a profit
If A is an investment broker.
However. . . .
B invests $100 with A expecting X return on the money.
But rather than growing the $100, A instead spends the money and takes money from C in order to pay B.
Can you say Bernie Madoff?
World English Dictionary
Ponzi scheme (ˈpɒnzɪ

— n
a fraudulent investment operation that pays quick returns to initial contributors using money from subsequent contributors rather than profit.
Now which of these two definitions looks more like Social Security?