This is an interesting discussion. I would love to see an episode of Time Team though I can't say I approve of using up historically important sites merely to make a few bucks on advertising. There are some twisted sensibilities involved there.

I think the problem between the metal detectors and the pros is a matter of educatioon and snobbery. The lowly metal detector goes out on a weekend to take the air and enjoy his hobby. There is a chance s/he'll find something valuable and that excites the blood.

What does each party consider valuable? Perhaps that is the main difference. The archaeologist considers the whole site in context. Why is artifact A lying in proximity to artifact B and how do these artifacts fit in with Professor X's theory of the the history of these people? Everything, from the layers of soil to the fragments of wood and pottery have meaning and need interpretation.

The metal detector just wants to dig up something interesting. It helps to know the history of the artifact because that makes it more valuable in his eyes. There is a big difference there.

You can't blame the archaeologist if he gets miffed because the sites have been disturbed.