Someone has always been able to "create money out of nothing." At some point there was no money; some time later there was. Someone or some group of people had to create the first money. People have actually "initialized" money many times throughout history e.g. when starting a country.
As long as you can separate "money" from its representation, there is nothing particularly problematic about some people being able to create money, at least some of the time. In fact it is necessary to provide money with liquidity as the economy grows and money is needed for more and more things (liquidity problems have triggered or worsened economic crises several times in history, especially when countries were trying to base their money on weights of metals).
Sounds like you are referring to the gold standard. A few things:
1. The dollar itself was created two centuries before the US left the gold standard. "Created" being the operative word. Created by Congress because America needed its own national currency.
2. Anyone who dug some gold up in their backyard was creating money when we were on the gold standard.
3. In 1862 paper money became legal tender in the USA without any guaranteed convertibility to any metal; that remained the situation until 1879. I.e. the government simply created money.
4. On January 31, 1934, the US dollar was devalued from $20.67 per gold ounce to $34. In other words money was created by an act of Congress.
Or to sum all that up for you: at a minimum Congress has always had the power to create money. All the metallic standards ever conceived of have been arbitrarily decided and governments have always had the ability to change the standard at will to create more money.
Actually, since 1777. For as long as the government is able to print paper currency instead of using metal coinage, it is able to make up as much money as it wants. Since not everyone is going to demand conversion to bullion, it generally doesn't matter--this is the principle behind fractional-reserve banking as well. If the government is caught out on printing too much money, then either the paper currency is accepted at less than face value (as happened to the original Continental Currency), or the government decides to suspend conversion (as most recently happened in 1971, but also in 1933).
What the OP meant by creating money out of nothing was fiat currency, which we do have now.
If you decide to use a commodity also as money, that's fundamentally different, and econ textbooks can confirm this for you.
T-Bills are backed by fiat currency, not by a commodity.
The Fed, and also the banks through fractional reserve banking, genuinely do create "money out of nothing."
Check out A Monetary History of the US by Milton Friedman and Anna Schwarz. Here you will find a Nobel Prize winning econonist who wanted to dramatically reign in, or even end, the Fed and get rid of fractional reserve banking.
Think about it again. You said T-Bills back currency today like gold used to, but that's not true. T-Bills are just notes to pay back more dollars. So it is dollars backed by dollars if you really are honest about your statement that USD is backed by an asset.
Not to mention that the value of a currency, like everything else, is driven by supply and demand; so in the face of fluctuating demand, adjusting the supply is necessary to ensure the currency measures a consistent amount of wealth, and doesn't inflate/crash.
As long as you can separate "money" from its representation, there is nothing particularly problematic about some people being able to create money, at least some of the time. In fact it is necessary to provide money with liquidity as the economy grows and money is needed for more and more things (liquidity problems have triggered or worsened economic crises several times in history, especially when countries were trying to base their money on weights of metals).