Well, actually the tribes view it as a compliment! One tribe said, “Our team name captures the best of who we are and who we can be by staying true to our history and honoring the deep and enduring values our name represents”. So they don't find it insulting. Information from Scholastic magazine "Honor or Insult?".

They say that cultural mascots are bad because they are an insult to tribes, but they are actually honoring the tribes because in North Dakota, the Fighting Sioux nickname is taken as a complement to the Sioux tribe. They said “I am very, very honored that they would use the name.” Therefore the names are not an insult, they make the tribes proud and feel honored. Information from the Scholastic magazine "Honor or Insult?"