I know some people who detect them, not personally, but people on other forums who ask permission and get permission. Now what they do is hunt all around, not over the actual grave. They detect where people got in and out of their buggies, or cars...depending on the age of the place. I see no problem with it. I do not think it is any different than detecting for civil war relics where people fought and died right on the battlefield and many were left right where they died. As long as someone is not digging up a grave, I see nothing wrong. But everyone has their own opinion.
I have had people ask me if I ever have detected at our local cemetary because it is so old and huge. They told me it would be a good place to go. And the people who suggested it were all elderly people. I just never have done it, not because I think it is wrong, I just don't want to upset anyone.
Now if I found an abandoned cemetary out in the woods or something I would detect all around it, no problem