"Since taxes are not voluntary, this creates built-in demand for the fiat money."

Not really.

The real underlying demand for a currency comes from the advantage that everyone gets by using the same currency in a common market.

The 'required for tax' purposes is a side-show.

Does anyone with any financial background appreciate that most businesses in the US want to use a single currency for their US transactions, and definitely not a 'grab bag' various currencies?

Nobody wants that. Nobody.

Also, the requirement to 'pay taxes' in a common currency is not coercive.

As long as there is liquidity in currency, then you can exchange whatever asset you want for USD and pay your taxes then.

Libertarians are still free to use whatever they want in their business dealings. Of course, we all use USD because it's pragmatic and useful.

"Capital controls are an artificial construct of the state"

Western nations do not really have 'capital controls' other than for the purposes of taxation and fraud. And sure, you could say 'taxation' is an 'construct of the state' but it's certainly not 'arbitrary'.

"When the money supply of your currency is not constrained (by gold, or otherwise), then it inevitably inflates, often unpredictably and uncontrollably."

Totally false. Inflation is a target by most central banks. They can make it positive or negative, generally, and target specifically 2% for certain reasons. You can argue against the 2% if you want, but not that managed currencies are inherently 'one thing or another'. They are whatever they are designed to do.

By having a 'perfectly hard currency' - you forgo the risk of having some crazy person doing monetary policy - but worse - you lose the possibility for having monetary policy altogether. How could you possibly not mention this as the most obvious drawback to a strict currency (i.e. no monetary policy)?

Monetary policy is a very powerful instrument for helping the economy along. Without it, it would be impossible to ensure enough liquidity as the market expands. Also, the economy would not be resilient to 'shock' events.

The reason zero economies on planet earth used a fixed-currency regime is because it does not work.

"The libertarian position on wealth inequality is that as long as the distribution of wealth was determined voluntarily"

This position is false, as capitalism itself is game of gaining leverage towards monopoly. Without some degree of redistributive taxation, 90% of the US economy would be in the hands of a small group of people. (And P.S. I'm no communist)

"Bitcoin is such a system: all participation in Bitcoin has been voluntary. "

Again, false.

Bitcoin is not a currency. If anything, BTC has proven how ridiculously bad this 'crypto-currency' idea has been as a currency. By it's very own 'relatively strict' status, it has increased it's value ('deflationary' in your terminology) - and has become useless as a currency.

-----> If we were using Bitcoin as a currency, the economy would be tanking due to a deflationary death-spiral <-----

EDIT: by 'death spiral' I'm referring to a common economic idea. As prices of goods go down, investors tend to hoard cash rather than invest it, as holding currency might be a better investment strategy than spending. Without investment, other parts of the economy slow, furthering the impetus to holding cash. The 'mass deflation' we've seen in BTC is equally as destructive as 'mass inflation' we would see from some really poorly managed gong-show currency.

Put another way: yes, you might like it if your 'new tennis shoes' were 1/2 price next week, and 1/2 that price the week after - hey - cheap tennis shoes! But think about it: has the economy just magically been 100% more productive each week? No. Of course not. So - what's happening is a monetary game that will soon hit your paycheque (i.e. your boss can pay you 1/2 your salary each week because that's your real market value). But worse - because of this drop in prices, your boss will be less likely to expand because his cost of capital equations show him it's smarter to hold the cash.

But it's all moot: Bitcoin is not a currency. It could be used as a currency, but it's not. It's just a purely speculative thing that's going on. People trading numbers for money 'because'. There's no rhyme or reason. There is no 'big government vs. small government' ideology here. There is no 'libertarian' behind BTC currency. It's just a meme with money that's interesting to watch.