How could something agreed upon be theft? If you know the inflation rate for ever, you agree on a possible (but not necessary) loss of value. It makes fiat inflation really different from Monero inflation.
Another innovative way to manage this with a predefined inflation rate is to use two units, one being the currency as usual, the other being the currency corrected from inflation. I only saw that in this "relative theory of money", only in French at the moment:
It's being experimented with an actual cryptocurrency:
Sommaire — Théorie Relative de la Monnaie v2.718
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Duniter is a blockchain software powering the Ğ1 libre currency.