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, this is a very good question. I read the comments on it, almost everyone agrees that there would be no point in buying bitcoin if it did not rise in price. This suggests that bitcoin will soon be a museum exhibit. It will not be able to constantly grow in price and therefore people will gradually switch to using other types of crypto currency, cheaper and more promising for growth in price.