Should cryptocurrencies be banned?

Should cryptocurrencies such as Bitcoin be banned?

For

 * Mining cryptocurrencies requires energy consumption and the result is creation of something redundant since 1) there are fiat currencies serving the purpose of a currency well and 2) those who fear irresponsible dealings with fiat currencies ("quantitative easing") can use gold as store of value, and no government can print gold.
 * Car racing or aircraft sport competition require energy consumption and are for pleasure, and there are alternative pleasurable activities. Thus, the argument suggests a much broader principle to be discussed, formulated and critically examined, and if that principle is accepted, it should be adopted rather than singling out cryptocurrencies.
 * The demand for increased electricity could increase investments in green energy such as wind and solar.
 * Proof of stake currencies such as Ethereum supposedly require far less energy than Proof of work such as Bitcoin.
 * The use of cryptocurrencies is an evasion of the state monopoly on currency. For that reason they should be illegal.
 * Other currencies, other "paper," precious metals, and barter also challenge such monopolies: should they be illegal?
 * Cryptocurrencies are much more useful to criminals than honest citizens and groups: they support tax evasion, black markets, and money laundering.
 * Such isn't always easy even with cryptocurrencies, or at least not much easier than with fiat currencies. If, for example, a dealer takes what he/she thinks is a kilogram of hashish from undercover police, it probably doesn't matter if payment is in bitcoin or cash.
 * Bitcoin is good for extortion, particularly in hijacking computers.
 * Those computers are probably vulnerable because measures to counter such are not employed—people should back up their data.

Against

 * People should be free to enter into contracts if they so choose. No one is forced to pay energy bills for cryptocurrency mining.
 * If fossil fuels are burned to provide the electricity, there's an environmental cost.
 * Cryptocurrencies provide incentives for advancement of chip performance: their mining creates demand for ever faster chips. Therefore, those who mine them in part finance faster chips for everyone.
 * In so far as the added demand for electricity increases electricity prices, the chip performance is funded by all energy consumers against their will.
 * This advancement concerns chips for dedicated special-purpose computers rather than for computers most people use.
 * That is not an objection as long as not only common-people computing is of value but rather also special-purpose computing is of value as well.
 * The increased demand for better Bitcoin-specific ASICs isn't necessarily incentivizing faster chips speeds, particularly for GPUs, but to make them even more specialized for Bitcoin mining. It's kind of like saying an increased demand for hypersonic missiles will help make far more turboprops in future go faster.
 * We should not ban cryptocurrencies using specific narrow reasoning unless we identify general principles involved and critically examine their undesirable consequences.
 * The free market will probably curb much of the abuses and excesses of cryptocurrency. Presumably people get cryptocurrencies for either (1) investing, (2) to insure against collapse of fiat currencies, and/or (3) black marketing. There are many things one can invest in, perhaps things more lucrative than cryptocurrencies; for those concerned about collapsing currencies, there are precious metals, commodities (non-perishable food, booze, bathroom tissue), and even other currencies—dollars, euros, and pounds probably have not inflated rapidly (i.e. more than 10% per annum) for decades; and the "crypto-"—i.e. the anonymity and secrecy—of cryptocurrencies is likely exaggerated.