"Depart from me for I am a sinful man."
Seeing Jesus as in touch with God and thus able to do miracles and seeing himself as out of touch with God and thus unclean and not able to much at all, Peter seems to be saying "Unclean! Unclean! My uncleanness with defile you." Jesus says, "Do not fear." Could he be saying "do not fear for my purity and cleanness; they are greater and more powerful than your uncleanness."
Perhaps Peter was used to being avoided by the "religious" people of his day for fear that his bad company would affect their good morals. Had Jesus gone away, Peter's presuppositions about religious people would have been confirmed, along with a profound sense of lostness of his behalf no doubt.
Peter seems to be saying, "Jesus, you don't want to hang round with me; I'm bad." Jesus doesn't argue with Peter's analysis, implying perhaps, "Yes, I don't want to hang around with you; I want you to hang around with me. No longer will life be on your terms. From now on life, love, liberty, etc will be on _my_ terms."
Peter's preuppositions were challenged: Jesus stayed and instead invited Peter to be a part of what he, Jesus, was doing. Jesus also invites us. No matter how foul we have become he does not recoil from us. And we are also able to reach out to sinners round us and invite them as Jesus did, to be involved in what Jesus is doing.