Maybe you weren't alive yet in the 60s, but it was an advancement because there had not been a scene on television before with a kiss on the lips between a white man and a black woman. There are some sources that dispute this moment, but that's why it was considered ground-breaking. Some stations refused to air it.
I was very much alive in the 60s. I am one-half of an interracial couple. I had to deal with a loving but disapproving mothers (on both sides). And just the other night I watched "Guess Who's Coming to Dinner" on TCM. I'm bona fide.
I would submit it was put out there and perpetuated by an unknowing media who, at the time, probably didn't know better and, because it is a point of trivia, no one has ever sought to investigate it - I mean, why would they ... its only TV show. Fans have kept the misinterpretation going because by definition they are fantical in their devotion.
I am of the type however that believes strongly that to accept credit or accolades where no credit or accolades are due is a form of lie. And since the kiss is nonconsentual and the result of force how can it be applauded or defined as anything other than "rape
I mean, in "Roots" when the plantation owner takes liberties with a "slave" should that be hailed as a positive interracial couple?
Now, to be clear, I am not saying Kirk was a rapist because he wasn't He was just as much a victim as Uhura.
The "why," the motivation, the intent is what frames something as being deserving or not of celebration. And it is the personal responsibilty of each of us to be principled in what we do or do not hold up for praise and publicity as to what Star Trek represents.
Would any of us show this scene to our sons or daughters to illustrate a positive human interaction? Speaking for myself, I wouldn't.