BTC is not an investment for stability [1]. And the OP is still asking a valid question, why pay BTC when that's several extra steps rather than pay debt or credit?
Mass adoption of bitcoin would certainly lower volatility, however bitcoin won't be massively accepted until volatility gets lower. It's a catch 22 game. So you are right, bitcoin doesn't seem such a good option for now, I was thinking a little bit down the road.
[1] http://www.coindesk.com/price/