You probably don't want to call them currency because you want to skirt the laws regarding currencies.
Diamonds are sought after as an ends unto themselves. People spend money to have diamonds, not to then turn around and trade those diamonds for other things. Diamonds can be used for jewelry, cutting things, etc. That's why diamonds are a commodity, while Bitcoins are a currency. If bitcoins were useful for anything OTHER THAN TRADE, you'd have a much better time trying to call them a commodity with a straight face.
And again -- it doesn't matter what the community calls them. Even if you could convince every person in the Bitcoin community to call them a commodity, it won't make a bit of difference. It's what the judge/jury/law defines as currencies that ultimately matters.
You are correct that I want to call them commodities because I don't want certain laws to apply to bitcoins. In the US Cash Transaction Reports (CTRs) and Suspicious Activity Reports (SARs) are a real hindrance to being able to transact in a free, anonymous and non-oppressed manner. If those same laws were to be applied to bitcoins it wouldn't outlaw bitcoins but it would make most people that use bitcoins outlaws if they failed to voluntary report such transactions.
Diamonds are not necessarily sought out as an end unto themselves except at the retail and industrial level. At the wholesale level people purchase them because they believe that they can sell them to someone else at a higher price.
Bitcoins do have a unique utility this being the ability to send them quickly, securely and without double spending and this is a unique and noble. Once exchanges begin to operate in an efficient manner this should allow a party to buy bitcoins using their native currency send those coins to a third party anywhere in the world and allow that party to sell those bitcoins in exchange for their native currency, with all of this happening in fewer than three hours. That is where the value lies with bitcoin, being the relative utility compared to any other method in regards to cost of transfer and the time it takes to make such a transfer.
In practice merchants would likely price their products at their native currency and then a bitcoin price where bitcoin price = native currency price/bitcoin exchange rate in that currency. Market efficiency should take over and make it so that the value of each currency relative to bitcoin closely follows the corresponding FOREX exchange rate.
It will be MUCH easier to persuade merchants to start accepting bitcoins if there is a liquid market where the merchant can exchange them for their native currency almost immediately after receiving them. Simply put businesses must turn a profit to remain viable and be able to pay their bills. Exchanges will be an integral part of the bitcoin economy until businesses can pay their lease, electric, internet and their suppliers with bitcoins.
Even if bitcoins were a semi-accepted form of payment the volatility inherent to the bitcoin market due to its small size necessitates that exchanges be in place if the acceptance of bitcoin was only relative to its value compared to a native currency. Plainly put if a company could pay their bills with bitcoins but they knew their bills were going to be 500 USD they would need to covert bitcoin to USD immediately upon receipt of the bitcoin if they wanted to stay in business due to the risk of ruin involved in being heavily invested in a very volatile market.
In a technical sense all miners are converting fiat currency to bitcoins as they are using their fiat currency to buy hardware and electricity to convert to bitcoins. If you actually can sit there with a straight face and tell me your computer is printing money there probably is not much I can say to dissuade you.
