Ask yourself this: Do you want to owe someone money because someone owed you money?
Maybe I do and maybe I don't. If I don't, Ripple doesn't force me to. If I do, Ripple lets me. You don't ever have to issue IOUs to use Ripple to make and receive payments. You need never owe anybody anything unless you find it to your advantage to do so.
Do you want to owe someone money because someone owed you money as another person owed that someone money?
Again, you need never owe anybody anything unless you find it to your advantage to do so. Read the very post you're replying to. Nobody but a gateway ever owes anybody anything in the typical payment paths.
Unless you like paying out of pocket for the mistakes and scams of others, ripple is destined to fail. There's no killer app for something that has a critical flaw in the logic, execution and pure greed of the developers.
You have to choose between the certainty of a small loss and the very low probability of a moderate loss. Today, every business that accepts credit cards chooses the former. If you do the numbers, the second makes more sense.