I was always taught that metal detectors are evil; the bane of archaeological research. The reason people said this was that so many sites had been robbed of metal objects, losing valuable contextual information in the process. Metal detectors are the key tool used by treasure hunters to quickly find and remove metal artifacts from archaeological sites for private gain.
However, more and more we find detectors being used to discover signals, allowing us to conduct non-invasive archaeology by plotting signal strength on maps.
Secondly, metal detectors are great for running over spoil heaps to find tiny objects that might have been missed by the diggers. By running a meta detector over discouloured soils we can discover evidence of smelting with ease.
Added to that is of course the joy of finding old coins, buckles, arrowheads and a million other artefacts.
With thought and care, there is no reason to reject metal detectorists and every reason to welcome them with open arms.