I have Native American ancestry--including Mohican and Cherokee--and I find it offensive as well. Believe it or not, the organization is a descendant of the Sons of Liberty that was created during the American Revolution. Obviously from the title they thought they could do things better than the Native Americans. Time taught us differently.
I don't understand why people think it's ok to dress up as Native Americans and pretend to be one. They don't dress up as Jews or Italians or Germans, do they? We're not a piece of history. We're part of the present. We're so part of the present that it was an Ojibwa man that created cloud technology that enables us to use all the electronic gadgets that we have.