No one guarantees the dollar value, but if you think about it no one guarantees the price for other things either. Other currencies, gold, silver, commodities - everything has some volatility. Gold is valuable because it is rare, does not deteriorate and all pure gold is equal. Industrial use exists of course, but it is minor in the grand scheme of things. Good crypto can have similar properties as gold, with the added benefit of being usable even for small amounts. I'd strongly advice against trading and speculating on a higher dollar value, but topping of a wallet with a few dollars worth for spending can be very useful.