My perspective on this is somewhat different. I was not raised in a tribe, but later was "adopted" or became an honorary member of a tribe. So while I do feel a deep attachment, I am still "white" (I put that in quotations as I do not like the labeling of individuals based on a supposed race or skin color, but it is a distinction people see). I have never been called a "redskin" or any other racial slur aimed at Native Americans, so I do not have that direct experience (even though I have seen such slurs directed at friends).
Personally then, I base my view on only what I can see and study. I do find the term "redskin" to be derogatory. I do find it a racial slur, and when it is used for a sports team, I find it very irresponsible. I don't think such use should be normalized, or even acceptable.
Looking at the earliest uses (at least by Europeans), the term was a racial slur, in much the same manner that the n-word was used towards Africans. It was a term to differentiate, and subjugate. Today, it is still often used in the same manner, as it qualifies a person by the color of their skin. And I don't think it is any surprise, but racism against Native Americans is still quite prevalent in the states.
I think terminology such as this, as well as naming teams with the use of a racial slur, only help cement this racism. It makes it normative, and justifies the use. It becomes a much larger problem when attached with a sports team, as it isn't just the name that become offensive, but the use of it. Such phrases such as "Kill the Redskins" or "Scalp the Redskins" are used regularly, which is not acceptable. The artwork that accompanies it (such as Native Americans being hung, or "cartoonish" pictures of Native Americans, which are often just stereotypical, racial depictions are often attached) makes the problem much more relevant.
So, I do not see the use of "redskin" to be acceptable. It was devised as a racial slur, and today, is often used to depict Native Americans (especially in the context of sports) in negative manners. And because of the continued use, I think it has largely become normative, which is a shame.