If it were guaranteed that the price of bitcoin would stay the same as it is today, would you still buy it? My guess is, the answer is no. But if its value lies in being a currency, price stability is essential. And if your answer is no, how is it then not just a Ponzi scheme? In other words, everyone is buying it on the hope of someone paying more for it in the future, not to use it as a currency.
Yes. It's a currency therefore i can buy and spend BTC knowing the value won't drop. I can use BTC when going abroad thus bypassing the need to use foreign exchange companies. Not everyone is an idiot like you who buy and hope to sell higher and make a quick profit in fiat terms. Fiat is constantly inflated and worth less over time.