It could be argued that the Federation is white America and all the face paint and prosthetics on the outsider races are stand-ins for blacks, Asians, the Third World, communism, the homeless, etc. I'm sure papers have been written on the subject.
As for the specific episode you mention, the "black guy goes for rape" argument can be made, but so can the one that goes, "he's not human, Klingons are just aggressive to the point of stupidity, Klingons are as different from humans as starfish are from giraffes." Of course, when the starfish and the giraffe are both obviously human, the issue is confused.
I usually just shrug and keep watching.
As for the specific episode you mention, the "black guy goes for rape" argument can be made, but so can the one that goes, "he's not human, Klingons are just aggressive to the point of stupidity, Klingons are as different from humans as starfish are from giraffes." Of course, when the starfish and the giraffe are both obviously human, the issue is confused.
I usually just shrug and keep watching.