Serious question:
If one is engaged in entirely legal activities - no money laundering, no drugs, no illegal weapons, no tax evasion, no slipping around international monetary controls - why would one want to use Bitcoin? With the volatility of Bitcoin's price, transfer costs of traditional payment methods (1-3%) are totally dwarfed by the risk of holding Bitcoins for even a short period of time. Maybe there is some opportunity for arbitrage in currency conversion rates, because of the low daily trading volume? But that doesn't seem like a likely profitable investment when you can lose 4% of your value at 3am because of a cascading margin call on a single exchange. Other than currency speculation and the ease of evading the law, why would anyone want to exchange a reasonably stable national currency for bitcoin?
Name me 10 currencies you'd be comfortable holding. It'll probably be very difficult. Fact is, billions use currencies with high inflation rates and with relatively short lifespans. And it's not just places like Zimbabwe that have many problems besides insane inflation the past decade. It's also relatively developed countries like Argentina that suffer from insane inflation. It's also small stable countries with a nice standard of living ($27k GDP PPP) with an educated population like Cyprus where many lost their savings as bank deposits were frozen or seized.
And that's just protection from governmental malfeasance that hundreds of millions have to be aware of. But it's also the fact that billions are unbanked. We at HN know more than anyone that providing a physical service (like mail delivery) is 1 million times more expensive than a digital service (like e-mail). Same for banking, for vaults, for ATMs, for services like lending, payments, remittance or money transfer. A digital version can be much cheaper, as well as more accessible. (for a bank you often need proof of identity, residence and employment. Good luck when you have no birth certificate, when you live in a slum, when you have an off-the-record job like selling fruit on the corner of the street). Digital banking can bring cheap financial services to hundreds of millions who don't have it, yet have (intermittent) access to networks as simple as SMS or radio, which can plug in to gateways to the bitcoin network.
Next up is us, the wealthy who enjoy relatively nice financial services. Bitcoin can save 1-3% in fees on any transaction. Imagine that there's a 1-3% tax on everything, not value added, everything, every transaction, whether B2C or B2B, and you have a way to remove that. That's very significant. Entire industries run on margins of 1-5%. Amazon's 2013 margin was 0.35%, imagine they could shave off even 0.5%.