The reality of SS is that the contributions you make into the program don't belong to you. The Supreme Court decided this, Flemming vs Nestor, some time ago. Moreover, Congress can change the rules anytime they want, e.g., in 1983 they changed the age for full benefits from 65 to 67.
Someone could pay into SS for 50 years, die the day before starting to collect benefits, and not receive a dime except for a small burial allowance. It is not a pension scheme nor does one's estate have any claim on one's contributions.
I agree, there is no legal individual ownership of amounts paid into the Social Security fund. There is, however, a current legal obligation to pay benefits at a specified level to qualified recipients. As with almost all government expenditures, Congress has the power to make changes or even eliminate the program entirely. There is such a thing as political reality and considering the size of the voting block dependent of Social Security, reduction or elimination of payments to current and imminent beneficiaries is about as likely as me riding my bicycle to the moon. As with the change of retirement age from 65 to 67, any further changes will be at the margins and will only impact future beneficiary who will have time to make other arrangements.