Picking up someone's bones, one thing. Picking up a piece of exploded ordnance, another.
I keep thinking if it were me, or a family member, would I want it (button, wallet, etc) to remain in the ground? Nope, I would prefer an individual to appreciate it, to give it further "life" with a new owner.
It has been mentioned already on numerous threads, today's museums, don't really want a lot of the items we, as military enthusiasts, collect. So why not have them in private hands (also previously mentioned). If the items remain in the ground, they simply decay, rot, and will never serve any type of purpose again. If I were to die on a battlefield, I would appreciate the surroundings and items to be used in some sort of useful manner rather than just fade away to history.
I believe this argument can be had for many war memorials, medals, artifacts. If I had say a VC awarded to my father, how long should the family hold onto it? If it were my VC won in battle, I would appreciate it if some family member down the line could put the fairly large some of money put to use, ie. down payment on a house, etc. The medal/award will remain alive, and probably more so, as the new owner will cherish, research and value it, as much, if not more than some distant family member who never laid eyes on me.
If given to some museum, it will stay in a box in the basement, never to see the light of day again. Might as well left it in the ground to turn to dust.
Different strokes, different opinions I guess.