SS is supposed to be like insurance, except that the managers of the government, at various times, use it much like Trump uses his foundation - as a slush fund for unrelated expenditures.
This is an eternal conservative meme, but it HAS NEVER HAPPENED. What SS has done is to invest in US T-Bills, which are the safest investment in the world. (Other governments even invest a lot of their money in them!) When you buy a T-Bill, the money goes in the general fund and the government spends it on lots of stuff. BUT THEY STILL HAVE THE T-BILL! Which SS can cash in anytime they need the money. (These are special T-Bills for SS only, with the same interest rates but the ability to cash in anytime.) You can actually go to the Washington, D.C. office of SS and see the T-Bills they keep in a vault.
It is an annuity rather than insurance, but operated as a non-profit. Commercial annuities are very much profit-oriented, which is the huge complaint about them. But there is nothing fundamentally wrong with them. In fact, most pensions operate in exactly the same way.
Right now, the "payin" and "payout" amounts are unbalanced because both are political hot potatoes. Nobody wants to fix it, because they might not get reelected. That's why all the predictions of insolvency. But all we really need to do is adjust a few things. Like keep the tax rate constant with no cutoff for the rich, or raise the full retirement age a few years.
