Artificially restricting the use as a currency because it doesn't work as a currency at the moment makes it a self-fulfilling prophecy.
Just imagine how sensible strong internet regulations would have been in 1992
Laws can be changed. If Bitcoin starts acting more like a currency, then the laws can be changed to suit. Right now, it is not very currency-like, and that is unlikely to change very much in the next five years or so, and so treating it as one doesn't make a lot of sense.
It's not quite like anything else, so why pigeonhole it? Call it a "decentralized cryptocurrency" or just "bitcoin" or "a perfect simulation of gold in electronic form"
If you brough gold bars into the country you'd be taxed in the same way.