Bitcoin has built in decay: inflation, high mining costs - whatever you want to call it - it's decay basically.
So the coin which should be used as a currency is unable to preserve value which makes it basically useless as currency because the main purpose of a currency is to hold some value relatively constant so it can be used in daily exchange of goods and services.
Please explain again why decay is an advantage for a currency and why anyone would accept a decaying currency in exchange for goods and services when presented with a choice between a more and a less decaying (and therefore volatile) currency.
Why would anyone choose the more decaying currency in an exchange of goods/services over a less decaying one - let alone invest in it?