I do let my dogs mouth gently — me but not the kids. Now that the kids are older they are allowed to gently mouth them as well. But they only do it when they are happy we’re home, mostly. Never in anger. In fact I don’t think our dogs ever get *angry* at a human being, because they know they don’t have the right.
Well, my dog is a mastiff. I don’t want him mouthing anything that doesn’t belong to him personally (food, bones, his toys, his blanket, his baskets, etc). He’s just too big, and an a nip could do real damage.