Rudolf Bultmann, the father of demythologization, urged people to get behind the text. On that, I agree. I also agree that sometimes the superstition of the age, or the need to see things in a miraculous way, can be passed down in an oral society much easier than it can today. But, I don’t think that is what is happening with the story of the fishes and the loaves.
At this point, I do not care if the event(s) actually happened. I don’t think that we can determine if Jesus set on a hilltop and fed even a single person, much less test the validity of the miracle. But, this doesn’t stop people from placing this story into two interpretative categories. One, it happened as the Gospels say it did. Twice. Or, we can demythologize it and suggest the real miracle is that people shared what they had. Perhaps, as the demyth camp suggests, this event tells us that when the one lone boy shared his meal, then the hearts of the others were opened.
Personally, I find it easier to believe that Jesus actually fed 5000 (Mark 6.30-44) and 4000 (mark 8.1-10) people via a miracle than it is to believe that the story is actually a mythologized account of a communal sharing of a meal because of the heart of a small child.
Rather, this section of Mark, as Adam Winn has established, is based on the Elijah-Elisha narratives. You cannot — you should not — read Mark without reading 2 Kings several dozen times.
Let me give you an alternative to the dichotomy of the “it happened” camp.
Mark is using two feeding stories to show that 1.) Jesus is greater than Elijah-Elisha and 2.) Jesus’ bread is better than the Pharisees. If you’ll turn to 2 Kings 4, there are 2 feeding stories there.
2 Kings 4.1-7 is about the plentiful oil Elisha grants the widow.
2 Kings 4.38-44 details the story of Elisha recognizing the poisoned stew, fixes it with yeast or flour. Then, it feeds more than expected.
In Mark 8.14-21, the disciples are hungry and ask for bread. Look at the answer Jesus gives them. Not only does he compare the bread he has with those of the Herodians and the Pharisees but he then calls attention to the number of baskets, as if they were a sign!
If you seek to rationalize the miracle you will miss the theological significance of them. They are crafted in such a way as to put Jesus into a particular place in the story — not only Mark’s story, but Israel’s story as well. Jesus assumes the Elijah-Elisha mantle, does it better, and then does it in such a way as to counter the opposing religious viewpoints.
Stop rationalizing, accepting, or rejecting the miracles. Understand how they fit into the story.