I'm not a fan of racial slurs and not very tolerant when exposed to it, but how many people can say that they've never uttered, typed, or texted anything in the last 10 years that wouldn't get thoroughly chastised in today's hyper sensitive world? I don't know anything about this DC and for all I know he deserved to get canned for his general body of work, but God help us all if someone decides to look at each of our pasts with a fine-tooth comb, has the freedom to cherry pick whatever moment of misguided commentary they could find in order to elicit the reaction they want, and then throws it up in front of today's hand-wringing crowd for "justice". First thought that went through my mind when I saw that was it was a pretty stupid thing to say/text on the part of the coach, second thought was that if all football coaches and players are going to be judged by this same criteria then we won't have many of either left, and third thing was to wonder who in the hell goes searching for 7 year old texts to find something like this and why? Our society seems to have a little bit of a witch hunt mentality that I find kind of weird.
I don't know about any of that, if only because I've never heard the n-word used in my entire life (live - I saw people say it on TV, etc.), and it's not like I grew up in a commune or in a PC household. I just knew through general media and popular culture back in the day that it was wrong, and neither my parents nor anyone else used it. It's just unimaginable to me anyone would write something like that it. More generally, I am in the legal field and more measured in what I'm out there saying or texting than most, I suppose.
Generally, though, I get your point about the witch hunt mentality. It's weird. Should a career be ruined based on a dumb text 7 years ago? You can argue either way. On the one hand, there is just no tolerance for racist behavior, nor should there be, and in his case, needing to relate to young men of color, he's pretty much blown that. On the other hand is your point, and there's something to that, at least for certain types of transgressions. In this case it's likely a moot point since if he wrote that, he probably was doing other racist things.
Much more significant to me, though, is how we simultaneously can be told what a terrible society we live in, with no progress made since times of open, widely-held and expressed racism, yet it's a national story when this guy sent one text using that word 7 years ago ... and his career is ruined as a result (he'll surely be canned). Seriously, think about this. America: a racist cesspool ... yet a place where it's national news, with a career ruined, for this lone private text with one word in it 7 years ago. Indeed, not only that, but the fact he sent that text several years ago is held out as evidence that America is a racist hellhole, too. That's the part that surprises me more than the mentality you describe.