21M bitcoins is a lot of bitcoins when you can divide them down into mBTC, uBTC, and Satoshis.
Ah, the point is not that "there wouldn't be enough of them". The point is that if you use a deflationary currency, you won't. You'll obtain a collectible that will be hodled and that will rise spectacularly in price, and which mainly becomes a speculative asset.
The problem is if you create too many, you get inflation.
The utility of digital currency for some may be the deflationary nature, but really only for those who have excess income.
For many of us, the utility is the ability to spend without tracking or over-sight of the corporate financial sector,
I don't need my bank knowing what I spend my money on. I don't need my bank denying a charge because they think it doesn't fit my profile of spending. I don't need my bank putting a 24-hour hold on funds I legitimately received. I don't need the IRS freezing my account.
Growing up, my dad took a second job as a LISP contractor and made some real bank. Unfortunately he did his own taxes and screwed up. Yup - our tax laws are so complex a LISP programmer has trouble figuring them out.
The IRS decided to audit and then suddenly froze all of his accounts, and after 9 months of haggling realized they also had made a mistake - Yup - our tax laws are so complex that our own IRS has trouble figuring them out - and realized that while Dad had underpaid them, it was not nearly the magnitude they had thought.
But for those nine months, we were really poor because all the assets were frozen - excess assets frozen.
Bitcoin, the IRS may be able to take my home but they can't take my accounts.
That's the value it has for me, it is free from government and banking tyranny and that is why I would rather spend bitcoin than use a fiat bank card.
With respect to bitcoin being deflationary, it is only deflationary if demand grows faster than supply. Other crypto-currencies have the potential to balance that out.
The problem is the majority of alternate crypto-currencies so far have been get rich schemes without developers qualified. However in the wake of bitcoin, more and more people are understanding block-chain technology and real alternatives to take some of the bitcoin demand will appear. Possibly even a fork of Bitcoin itself if the BU forks but blockstream loyalists keep using the 1MB chain.