If most of us use Bitcoin for investment purposes, Bitcoin value will be always volatile, not stable. Except, all of us agree to use Bitcoin for payment tools only, this may lead to a stable price then. Logically, no investors have the intention to see their assets have stable prices, how they can gain profits? Moreover, there are too many whales or big investors in Bitcoin, that's another sign that Bitcoin will exist as a digital investment for a long time. They mostly prefer to hold for years. Another reason, Bitcoin isn't centralized, so it is difficult to control its value around the world.
Absolutely true, without market volatility there will be no entry and exit for investors and no profit making. When the price of btc is down new investors have the opportunity to come in or sell when the price is at the peak.
Right now, people are more interested in making money with btc than paying bills with it.