I am a big supporter of crypto currencies, and I do see a problem in that. However, the current volatility will level off significantly once there is wider adoption. That will help reduce incentive to hold. I would never recommend somebody give/accept loans in crypto currencies right now. The time will come though (unless governments squash crypto through regulation or outright banning).

That said, there's no guarantee that BTC or any crypto will appreciate indefinitely; in fact quite the opposite. It can (and does) lose value.

This also overlooks the benefits of a non-fiat currency, such as protection against things like hyper-inflation (most of us don't think about this right now, but if you have any friends in Venezuela ask them how important this protection is).