I ask somebody how probably has no idea of cryptocurrencies.

I ask him: imagine there is a currency where you have pay for having money.
He reponded: ah, demurrage.
I ask further: what could somebody encourage to buy such money?
He basically said:
1) if my purchasing power in that system increases more than the demurrage reduces my money
2) if there is some [service] I really want or if I really want to offer a [service] there because when I do not somebody else will and I will lose profit