[Y_Y]

Your idea is interesting, but there are plenty of justifications given for governments setting positive inflation targets. Assuming they can control e.g. public sector wages and export competitiveness by another means, how do you prevent people being disincentived to spend or borrow money?

[nine_k]

Have you considered that people (1) need and want to consume and (2) want to invest into things that bring in more money, and/or other goods?

Forcing people to consume and invest, because else the money will expire, leads to mindless consumption, reckless unwise investment, and the lack of safety nets provided by savings.