I think the confusion is that they believe the token that is staked is a sunk cost, the same way a business would spend the money from a loan. Like you said, the token will be returned when unstaked.
If I take a loan out to buy and run a pizza restaurant, I can't just give the principal back if it fails. I would have to liquidate the business, which would not be equivalent to the starting capital costs.
The Fed always can return the money, because they control how much money is printed. Therefore, the money loaned to the Fed through the overnight rate is risk-free. That's why its called the risk-free rate.
It may only be a singular day worth of bond / IOU, but its still a loan/bond/debt instrument.
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Similarly, the Ethereum rewards are printed out of thin air, are they not? By the Ethereum staking system? Its not like the Ethereum they print existed beforehand.
If I take a loan out to buy and run a pizza restaurant, I can't just give the principal back if it fails. I would have to liquidate the business, which would not be equivalent to the starting capital costs.