Let me just go ahead and quote myself:
The whole idea of why Hobbits carry the ring is that, the ring is a powerful item and Sauron, being powerful himself made it. He expects someone powerful to want to carry the ring, or at least a force powerful enough to face the hazards of Mordor. That's the genius of the plan to let Frodo take it with him. It could never in a million years occur to Sauron that a tiny hobbit will sneak into Mordor with the ring. It is inconceivable to Sauron that ANYONE, even his enemies, could give the most powerful magical artifact in all of Middle-Earth to such a frail, weak, and small creature. He expects his enemies to fight over the ring because of it's power. But that would be their undoing. Since the ring corrupts ones power, the more one has, the more evil and destructive one can become. Since the Hobbits had little but their courage and heart it allowed them to carry the ring without being corrupted or noticed. At first you might say they should have flown there or at least that the plan is stupid. But in actuality it was the ONLY plan that could ever have worked.