The system encourages and forces you to do exactly that.

If a person doesn't like the idea of debt or inter-personal IOUs then no one is forcing them to use them with Ripple. A person can fully use Ripple only ever trusting a single gateway the same way they trust a bitcoin exchange. Including, if they want, (as some have suggested) only leaving their funds in Ripple as long as they need to use the service (for conversion or for making/receiving payments). If someone thinks that's still bad then I hope they speak out just as loudly against all the bitcoin exchanges that are giving people internal IOUs for their USD and BTC deposits (and in many cases those IOUs are not transferable).