Yes and no. It has become more "welfare-like" in recent years, but it was orginally sold as "insurance." Its offical name is OASDI - Old Age, Survivors, and Disability Insurance. Everyone was told that if you put money into it, you would receive benefits after retirement, if disabled, or your survivors would. It still works that way, for the most part.
This is not to say I think it's a good program. I wish it were never created. But it's here and I paid a small fortune into it and I want some of it back. And I'm not going to sit quietly and say to the government, "Here. Just take it all. I don't want it." My age peers are not likely to do that, either.
I like to think that my insistence that I receive benefits when I retire is my way of helping them keep their word.
If, however, you die in the first month of your eligibility and you leave no minor children and have no wife all benefits cease to exist. Even a widow will only receive half of your monthly payment iof whe is not eligible by virtue of her own employment.
It is, in sum and total, a welfare program. There is no fund and you have no accrued account.