Yep. Nothing racist about casting all black actors as this barbaric race, is there?
I don't think that's fair, because we've seen dozens of alien races in Trek that were just as "barbaric" and were played by all-white actors. The Capellans in "Friday's Child" spring to mind just off the top of my head. And sticking just to the first season of TNG, we have the Bandi in "Encounter at Farpoint" (a technologically backward people enslaving and torturing an innocent alien), the murderous and warlike Anticans and Selay of "Lonely Among Us" (played under their makeup by white actors like Marc Alaimo and John Durbin), the oppressive matriarchy of Angel One, the wartorn Mordanians of "Too Short a Season," the child-abducting Aldeans of "When the Bough Breaks," the ruthless Minosian arms dealer in "The Arsenal of Freedom," the drug-dealer Brekkians of "Symbiosis," and the Romulans of "The Neutral Zone" -- all guilty of "barbaric" behavior, all played by white actors.
It's just the nature of an episodic space-adventure series that the majority of aliens the cast encounters are going to be antagonistic in one way or another. So if you refused to cast nonwhite actors as villains, you'd give them fewer opportunities to play a part in the series at all. Like I said, in 1987 it was rare for aliens to be played by black people at all
. Lando Calrissian was about it. However problematic it may appear now, at the time it was actually a small step forward, even if it did turn out to be a misstep. This is the nature of progress. What seems progressive at an early stage (like the miniskirts of the TOS women's uniforms) comes to be seen as backward later on when society has progressed well beyond it.
And Trek did improve on it later on, of course. In addition to having Michael Dorn as the featured Klingon (even if he did fall into the "angry black man" stereotype to an unfortunate degree, at least until DS9 started writing him better), we got increasingly multiethnic casting for major alien races like Klingons, Romulans, Cardassians, Vulcans, and Bajorans.