Those nicknames automatically project an aura of pride and strength. As tribe names, they project an aura of respect and promote the traditions of those tribes. The term is a slur toward American Indians-there is no other connotation. Pick any ethnic or racial slur and replace Redskins. There is no rational argument for the term Redskins NOT being a racial slur.
Some terms can be acceptable.
Some slurs can never be acceptable. The next move for the city leaders is to insert the confederate flag on the town seal and the town's street signs. It's only a natural progression. One particularly clueless student decided to show up at the board meeting wearing stereotypical Indian-garb. So basically he revealed that the students love and respect a racial and ethnic slur.