Here's my problem with the "history" argument- It's basically just rewarding being so stubborn, out of touch, and arrogant to hold strong to a racist nickname or a racist logo or whatever for far too long. Just because you've done something wrong a long time, doesn't mean the onus is on others to just accept it.
Here's my problem with the "Native American's are fine with it" argument - I don't believe racial slurs, racist jokes, hate speech, etc. are wrong just because they offend those they are directed at. If I had a kid and he pointed out an African-American and said "look dad a n-----," I wouldn't feel like it was okay so long as no African-Americans heard it. Crap like the Redskins or Chief Wahoo offend my sense of decency, and I'm not any part Native American. Same way I feel when I see old racist caricatures, literature, etc. There's a reason we try to bury so much of it in the past, because it hurts to look at now, and that's how a lot of people feel about these teams.
The change is inevitable, it WILL happen, people are not going to grow more accepting of ugly racist relics on grand display over time.