Can you explain the "create competition" claim of the public option? [View All]

[WhaTHellsgoingonhere]

This remains an elusive concept that has yet to be explained fully as far as I can discern. The public option will be available to those who currently don't have insurance, be they healthy or otherwise. For them, this is great news. But those who have employer based insurance were never competing against those without. How, then, does creating a new pool that doesn't compete with the existing pool put downword pressure on private insures? Simply, apples don't compete with tennis balls.

There's a disconnect. I just haven't found anything that will explain this.