Personally I have no problem with people owning MDs.
I am sure every detectorist would feel that they have a 'right of ownership' as well as a 'right to detect' with a MD. I can agree with them with this matter as either way their 'rights' aren't illegal.
Ownership and use of metal detectors like many other activities in society have their restrictions.
For example one might own a horse and enjoy rides in the countryside. One might feel that one has a right to own and ride a horse and there IS nothing wrong with that as it is quite legal to do so. However when out riding in the countryside you just can't go anywhere and one has to keep to roads, bridleways, public land, and not public paths and private land.
Just because it may be legal to own something does not give one the right to rampage across the landscape at will.