No one "raided" the trust fund. There was never any real "money" in it in the first place because that's how bonds work. Bonds destroy money in the private sector, erasing it against the debt (our money supply), so it can't then "fund" anything. They are a promise of future payment and must be remonitized when they mature with new money creation.

The only thing accomplished by collecting payroll taxes is reducing the worker's spending power at the moment. This was important when we did that gold standard silliness, but it isn't applicable to fiat system in terms of future benefit payout.