If you notice that your money is worth more tomorrow, you are going to save your money and spend it tomorrow. This is true in situations of "deflation".
This sounds good to you, because all you have to do is wait and you'll be better off tomorrow. You don't even have to work to get more stuff.
However, you aren't the only person with this idea. Everyone saves their money in the bank. The people who sell goods and services, sell fewer goods, and maybe go out of business.
The economy slows down.
On the other side, if you design an economy so that inflation exists. People want to spend because in the future their money will be worth (a little bit) less.
Money flows around a lot. People who sells things make money and stay in business. People have jobs and the money is still worth something.
Remember money isn't worth something, trading good fluidly and efficiently is worth something. Money lets us do that. So a currency that lets us do that is good.
If anyone knows more about the situation, please add it. I don't know any economists so this story is probably pretty incomplete.
(Of course the macroeconomic recession-proof nature of demurrage currency makes it desirable for merchants as well, and the zero-interest loans are a boon for entrepreneurship. I'm just saying even if you're skeptical, that shouldn't be a barrier to acceptance.)
When we say zero-interest, we're talking about basic interest/liquidity premium: the interest which is attached to loans simply because of the opportunity cost of lending, not the risk taken on.
As this hasn't happened, it may be worth considering the effects of time preference in both examples.
Even if you are correct and the existence of gold is detrimental to the economy, I don't see how you can prevent the effects of an existing devaluating currency/commodity by creating a new inflating one.
See
www.slate.com/articles/life/holidays/2004/12/what_i_like_about_scrooge.html
I suspect few rich people keep their riches in cash.
I recommend reading David Graeber's "Debt: The First 5,000 Years". IIRC it has a good chapter on demurrage, as well as covering many historical currencies which by accident of design were similar to modern demurrage currency in operation.
By adding a component of inflation, you increase exchanges.
Let's just get rid of the cap and keep things simple.
edit: Of course from a micro-economic perspective this doesn't make sense unless it was forced onto us by a government as a de facto standard.