You're not real clear on how the Social Security trust fund works, are you?
Here's a primer for you. Check out page 5, especially step 4). That's the step where the money collected from the SS taxes that isn't paid directly to the beneficiaries is invested; the surplus that accumulated is held in a "trust fund" and *invested*. Smart, right? It would be reckless and stupid to just store that money under the mattress or in a vault, losing value due to inflation, right?
What's the safest investment in the world? That's right, US Treasury bonds. That's what the were invested in. Not the highest return, just the most secure choice that has a return. Now, when the cash is "given" to the US Treasury by the Social Security Administration, the US Treasury gives the Social Security Administration a bond, a promise to repay the money, plus some interest. And the US Treasury gets the money, to spend. That's how much of the government's cash flow works, and you're not complaining about that. So let's just leave that alone.
Back to the SS trust fund. Actually, the government, the SS Administration, they *do* spend the money. They pay it out to the beneficiaries. But you probably meant some other part of the government. Regardless, there is no part of the government, apart from the SS Administration that has spent the money of the trust fund.
So... I don't know what you're complaining about.