There being a cap is relevant, because it makes your currency deflationary and therefore a poor medium for exchange and a very poor medium to base an economy ar

There being a cap is relevant, because it makes your currency deflationary and therefore a poor medium for exchange and a very poor medium to base an economy around (as, among other things, it increases the real value of a debt over time and discourages investment). Small amount of deflation are dangerous - but if everybody used BTC for everything the deflation would be massive and the effects severe.