There is a predictable deflationary curve if you want to think of it as a currency - it is consistently going up in value.
You conflate two different concepts. There is no doubt that the number of Bitcoins is increasing on a predictable curve - by definition that is an "inflation" of the currency. Do not confuse that with a rise in the purchasing power of the currency and the consequent drop in the price of goods and services as priced in BTC.
But you are right that it is also deflationary, just not in the way in which you think. It is my understanding that Bitcoins can be irretrievably lost. Eventually, after all the Bitcoins have been mined, the number of Bitcoins in existence will start to fall (in other words, the currency will deflate, however slightly).
If your currency's value goes up over the long term, it encourages hoarding and discourages productive economic activity.
It's hard to believe that people actually think this way, but a century of central banking propaganda has had its intended effect.
Though certainly true that rapid fluctuations in a currency's value make it inconvenient as a medium of exchange (the problem with BTC right now), a rise in the value of a currency rewards savers and increases the pool of savings available for investment in productive economic activity at lower interest rates. An endlessly inflated fiat currency has the opposite effect: it encourages malinvestment in unproductive economic activity (also known as "bubbles" - e.g., internet stocks and real estate), punishing savers and rewarding debtors. Though interest rates can be kept artificially low for a time, eventually either interest rates must rise or the value of the currency must fall (or even both).