Poor Little Robin

For a man that moaned so much at being alone and marooned on an island, I find it incredible that his first reaction to finding some evidence of another human is an irrational panicked flight back to his 'castle.'  I readily grant that the person could have been unfriendly and violent, and it would have been prudent to make sure that Robinson sees the intruder to his 'kingdom' before the stranger sees him. Ironically, as we have just spent a significant amount of time having Robinson's newfound faith expounded to us, he immediately thinks the devil must have set foot on the island. Really? You can spend years developing a system of creating clay pots without any prior knowledge, but you spend those same years diligently studying the bible and automatically the devil has come to test your faith?
In all honesty Robinson seems almost reluctant to leave his solitary life. As he notes earlier, "I was removed from all the wickedness of the world here.... for I had all that I was no capable of enjoying." Indeed, he has food to eat, a dry shelter, and pets for company, all painstakingly earned with hard labor and sweat. For all his initial rage that he might die in the storm, or starve on the shore, Crusoe has found that this life suits him better than civilization. Going back to his conversations with his father about finding happiness in life in the lower middle class of people, his father tells him that in this group he should have income enough to pursue any diversion he should desire, but without the jealousy, envy, and greed so common to the upper class. Clearly, Robinson finds this unappealing, and I wonder if, in becoming an archetypal self sufficient pioneer, has he not found the 'class' that his father told him of?
He is told that only the truly adventurous rich man, or the truly desperate peasant, strike out into the new world. Those in the middle stay right where they are at, beause they have no enough to gain, and too much to lose in a gamble like that. Think of the many times that Robinson mentions the money he saved from the ship and how uttlerly useless it is to him on his island. I wonder at the meaning of the passage where he talks about how much he would pay for some of the smallest conveniences of the old world, and yet how he manages to eventually make the pipe that he wanted to badly, or the clothes that he was missing. It is as if, given enough time, and nothing else to divert the attention span, a person might well teach to themselve any number of useful skills and can in fact be an island unto themself. I am wondering if Defoe here is intimating that civilization might produce more out of its people, but a sort of law of diminishing returns goes into effect as each person needs to produce less to survive, then they will. Now I recognize that Crusoe eventually has companions, but how telling is his initial reaction to evidence of another human? How much has he grown to love that he is niether high, low, nor middle in the strata of humans?