In the 11th century, when many of these churches and cathedrals date to, there was a distinct class divide between the peasant builders and stonewrights who built these structures, and the clergy who resided and instructed in them. Thus there was always an element of mistrust, since all that the lower classes knew of Christianity is what the educated, well-fed, and wealthy clergy told them. The vicar I knew at Harlaxton described it this way; "The Green Man was insurance," he told me. "The people who built these churches were not convinced that they would go to heaven, just because the priests told them so." If they did, then they could point to the cathedral they built and say to God, "Look what I built for you." But if the priests were wrong, and the builders ended up in the other place, they could point to the Green Man carved in the rafters and say "You're there too."
The point of this history lesson? I'm thankful that we live in a day and age where we have access to the Scriptures and can know for our own certainty that God loves us, and wishes to save us from our sins. Jesus Christ is our insurance policy, with the premiums paid and the deductible satisfied. Thanks to men like Gutenberg and Luther, we do not need to rely on a clergy class that we mistrust to tell us this.
And the Green Man? He's still there, amusing onlookers and scholars alike; for like other images of carven stone, he had to be lifted into place, and remains impotent.