Assumes facts not in evidence.
Social Security United States - Wikipedia the free encyclopedia
Then there is the language of the Social Security Act itself;
Social Security History II
TITLE II-FEDERAL OLD-AGE BENEFITS OLD-AGE RESERVE ACCOUNT
Section 201. (a) There is hereby created an account in the Treasury of the United States to be known as the Old-Age Reserve Account hereinafter in this title called the Account. There is hereby authorized to be appropriated to the Account for each fiscal year, beginning with the fiscal year ending June 30, 1937, an amount sufficient as an annual premium to provide for the payments required under this title, such amount to be determined on a reserve basis in accordance with accepted actuarial principles, and based upon such tables of mortality as the Secretary of the Treasury shall from time to time adopt, and upon an interest rate of 3 per centum per annum compounded annually. The Secretary of the Treasury shall submit annually to the Bureau of the Budget an estimate of the appropriations to be made to the Account.
OLD-AGE BENEFIT PAYMENTS
SEC. 202. (a) Every qualified individual (as defined in section 210) shall be entitled to receive, with respect to the period beginning on the date he attains the age of sixty-five, or on January 1, 1942, whichever is the later, and ending on the date of his death, an old-age benefit (payable as nearly as practicable in equal monthly installments) as follows:
Note the use of standard insurance industry terminology such as "actuarial principles", "tables of mortality", "qualified individual", "benefit", "payable" and "monthly installments".
Funding is irrelevant. The concept of Social Security is as an Insurance program designed to ensure that the elderly don't end up in abject poverty when they can no longer work. The reason that it is mandatory is because it doesn't work otherwise.
Calling it an "entitlement" is disingenuous. No one is "entitled" to social security unless they, or their parent or spouse, has met the requirements for receiving benefits.
Social Security is one of the longest running and successful programs of it's kind in the civilized world.