Bitcoins primary purposes today consist of: 1. buying bitcoins in the hope that they're worth more tomorrow, and 2. using bitcoins to buy illegal drugs on the internet. And the only reason #2 is declining is because so many people are doing #1 that it's getting too expensive in terms of fees to use it for #2.
> In terms of energy, this can be a criticism of almost all currencies and stores of value.
You're comparing fixed, one-time capital costs with ongoing variable costs. Transferring gold from one human to another involved handing it over. No costs there. Transferring bitcoins requires an increasing amount of energy as the rules make it harder and harder to complete a block.
> Manipulation and price swings are a valid concern, but no other currency is immune to those either.
When was the last time your USD bank account suddenly became worth twice as much, or half as much? Central banks can utilize price control mechanisms to carefully maintain inflation rates. Most aim for 2% per year, and most hit their targets pretty accurately. Bitcoin cannot offer that.
