Make up your mind already!
I think the problem is that it's actually both. It can be used as a currency to pay for items and or to send to others just as you would with fiat. Its however also a commodity like gold as many acquire it with the intent of holding onto it waiting for it to appreciate in value leading to an actual capital gain being made and thus the reason for wanting to tax it for capital gains tax.
I'm don't think all countries will ever reach consensus on how to handle bitcoin. Best solution I can think of is that its treated in accordance with how it was used but this is another can of worms.