Why did you make the inference that Dr. Kelton, or any MMT economist, supports UBI? There may be a couple of them, but the vast majority of economists supporting MMT perspectives don't support such a program and for many of the reasons you identified.
Also, if the only thing you took from Dr. Kelton's book was "printing money" you have a problem with reading comprehension (if you read it).
According to the author, the Federal Reserve, on behalf of the US government, can print unlimited amount of money and give it to the government for free to spend as the policy makers wish. In fact, even if the Fed charged an interest rate, that should not be a problem. The Fed is legally obligated to return the interest earned back to the government, which essentially makes the impact of any interest rate meaningless
Does your bank "loan" you money in your checking account, or does it simply record positive and negative transactions that affect your balance? Congress "creates" money when it authorizes spending in the private sector and the Fed simply acts as the clearing bank for payments and receipts.
No one can "loan" money that doesn't exist and the only Constitutionally authorized entity that can create new monetary assets in the US is Congress. This is why MMT economists never view taxation or borrowing as "funding mechanisms".
So, the issue with UBI is not the magnitude of the money supply itself, but rather how to manage the overall flow of money to prevent the whole UBI initiative from becoming counter-productive. Therefore, fiscal balancing is necessary to prevent wealth inequality and someone must pay for UBI— either now or in future. Running large deficits eternally is unsustainable.
While your assertions are close to fiscal reality, they are far enough off target to cause major damage to the economy. The federal government, specifically Congress, is the only "net" source of monetary assets the private sector has. This means that "balancing" the budget would effectively steal the resource and labor the government sector demands and uses, leaving no payment for those in the private sector as a store of value.
This is, and has always been, as unsustainable as inflation caused by overspending. The last seven times the budget was balanced for any length of time resulted in recessions or depressions and greatly increased default of private sector bank debt. Coincidence doesn't imply causation, but "every damn time" is certainly a persuasive argument. This is largely due to the fact that only public money can "net" retire private debt or be "net" saved without incurring increased private debt.
