There is much evidence to show that it was not a realistic portrayal of the subject matter, even in the late sixties, and that it is even less recognisable now. But Guess Who's Coming To Dinner is not documentary, or even that later invention; docudrama. It is theatre, and in the theatre, characters are given a point of view, a goal, and obstacles.( Notice that reality is not a prerequisite for any of these.)
So given that we are watching art, what can we say about it? Well we can say that this film contains some of the strongest performances ever committed to celuloid; Spencer Tracy, Katherine Hepburn, Sidney Poitier. Katherine Houghton sings more softly for she carries the torch for youth and innocence (supposedly representing the generation that does away with racism - from 40 years on how we wish that THAT at least were true!)
But even if you think you know the story, and you think there's no reason to see it because it is so dated, BUY THIS DISC and add it to your collection for the performance of a lifetime: Beah Richards as Mrs. Prentice (Sidney's mom) will, in the middle of a movie designed to make you think, reach right into the center of your being and break your heart, just as her's is breaking. Her scenes bring this movie to a higher level - high and deserved praise seeing as Tracy and Hepburn set the bar.
It wasn't meant to cure the evil. It, in truth, hardly acknowledges the evil of racism (perhaps the most valid criticism that can be made) but it did, in it's time, a miraculous thing: it answered the question "Is it wrong for men and women of different races to marry?" -
the answer, simply,: "No."