I have spent a good dela of time pondering the what and why of megalithic structures. To some extent I think they were a statement of what could be achieved. Whenever man harnesses a technology, he pushes it to the limits. Pyramids, henges, cathedrals, bridges, and skyscrapers are all examples of people showing how far they can go with their particular technology.

Stone was the raw material of the megalith builders. To begin with it furnished them with tools that enabled them to achieve mastery over their hostile world with knives, axes, and arrow heads. As they discovered methods to manipulated bigger and bigger stones, they were symbolically achieving dominance over the very earth itself and they wanted to express that in a powerful way. Building a massive stone circle is just such a statement. It says "Look how powerful we are".

I imagine that these statements of achievement would be tightly incorporated into their religious beliefs, so I tend to agree with Fourwinds that the sites would have had a predominantly ritual function.

In some ways it's not too different from modern religions where people glorify their god with human achievement while at the same time investing their god with their own specific aspirations. Religion is just another tool to manipulate the world. "The will of God" is nothing of the sort. It's the will of some person or group. I think Neolithic people may have had an attitude something like:

"We can manipulate the stones. We can make them stand up when by themselves they fall over. See how we command the earth spirits to rise up and do our bidding. We are the chosen ones. The true believers."

It might be a good idea to question what we are calling trade. Axes for example may not have been anything like the trade goods that we commonly think of, it may be that the procurement of the axe may have been an integral part a the quest that took people across the country in an effort to appease the gods. I wonder exactly how much design variance there is with axes of a particular type, that might give some confirmation that they were many produced by a few, or more individually created.