What about the Minnesota Vikings? Their name and logo could be construed as offensive to Scandinavians.
The difference between the Vikings and the Celtics on the one hand, and the Redskins on the other, is that the Vikings and Celtics are home teams of large Scandinavian and Irish communities, so were chosen to represent those communities with pride.
In the case of the Redskins, it was plucking a completely different nation's identity, choosing an offensive term, and using it as a mascot.
That's problematic as well.
So Native Americans are a different nation from other Americans?