Stable currencies do not increase in value the way Bitcoin has over the last several months, which increases the chances of a crash in its value. One of the points made in the Economist article I cited above is that, if Ripple gains traction, it would likely cause a big drop in Bitcoin value.

Recent article in Economist about Bitcoin gives some background about Ripple: http://www.economist.com/news/finance-and-economics/21576149-even-if-it-crashes-bitcoin-may-make-dent-financial-world-mining-digital

as above