Let me start from the beginning -
A long time ago before you light skinned, light eyed folk showed up, we indians were living it up in the good ol' U.S.of I. (united states of Indians)
We had just emerged from the previous world and were visited by the Holy People who walk the rainbow path. They gave us the twelve teachings and dwelled in the four sacred mountains while we set up for business. The Holy People chose individuals among the populace to be messengers. With this title they were given very powerful gifts. shape change, run as fast as the wind, become shadow, be impervious to weapons, and many other "things." When they wore the skins of animals they took on their attributes but still keeping the human awareness. This made them very powerful. When it came time for the Holy People to leave they called the messengers to them and asked for the gifts to be returned (this was known from the beginning that they wouldn't be able to keep them). Quite a few of them became selfish and envious and chose to keep their gifts and ran away. They have followed a path of chaos ever since. They recruited people to become skinwalkers by luring them with power and prestige. To become one you had to kill a person with gifts (medicine man) or a family member, showing that nothing is more important than the way of naagloshi. It has been an ongoing battle ever since. The person next to you could be a skinwalker and you wouldn't know it unless you were gifted. I have a cousin who is a handtrembler and he always knows. Sometimes you can spot one by the knots in their hair... they tie small knots in thier hair.
I can only be responsible for my own "hozho" (harmony/balance/beauty) I cannot bring harmony to anyone else. I can be an example but I can't influence them one way or the other. These naagloshi/ma'ii tsoh made their choice a long time ago. They know the consequences. Only they can bring themselves back to hozho... no one else can.